Login In
2017 Volume 75 Issue 1
2017, 75(1): 5-6
doi: 10.6023/A1701E001
Abstract:
2017, 75(1): 15-21
doi: 10.6023/A16080417
Abstract:
In recent years, visible-light-promoted photoredox catalytic activation of organic molecules has been flourishing vigorously. This kind of methodology usually takes advantage of transition-metal complexes and organic dyes as photosensitizers, which can directly react with organic substrates through a single-electron-transfer (SET) progress under visible light irradiation. It's operable to construct C-X (X=C, N, O …) bond via the radical or radical ion generated during the SET process. On the basis of different key intermediates, this highlight gives a brief summary on the recent development of visible light promoted benzylic Csp3-H activation and functionalization.
In recent years, visible-light-promoted photoredox catalytic activation of organic molecules has been flourishing vigorously. This kind of methodology usually takes advantage of transition-metal complexes and organic dyes as photosensitizers, which can directly react with organic substrates through a single-electron-transfer (SET) progress under visible light irradiation. It's operable to construct C-X (X=C, N, O …) bond via the radical or radical ion generated during the SET process. On the basis of different key intermediates, this highlight gives a brief summary on the recent development of visible light promoted benzylic Csp3-H activation and functionalization.
2017, 75(1): 22-33
doi: 10.6023/A16080418
Abstract:
Enantioselective control of free radical reactions has eluded organic chemists for decades. Echoed with the renaissance of photo-induced processes, or so called photocatalysis or photoredox catalysis in organic synthesis, photo-induced organic radical chemistry has regained its prominence in developing catalytic asymmetric radical reaction. The generally mild conditions inherited with photochemistry, particularly visible light photo-processes, have allowed for controllable generation of free radicals as well as the subsequent bond formations. The past five years have witnessed dramatic advances in exploring photo-induced catalytic asymmetric free radical reactions, and enormous potentials along this line are envisaged. This perspective gives a brief summary on the important advances in this field. Accordingly, the major advances are classified based on different radical species including α-amino/oxyl radicals, radicals generated from enones and its analogues, benzyl radicals, α-carbonyl radicals, polyhalogenated alkyl radicals and nitrogen radicals. Brief discussion of mechanism is presented whenever relevant.
Enantioselective control of free radical reactions has eluded organic chemists for decades. Echoed with the renaissance of photo-induced processes, or so called photocatalysis or photoredox catalysis in organic synthesis, photo-induced organic radical chemistry has regained its prominence in developing catalytic asymmetric radical reaction. The generally mild conditions inherited with photochemistry, particularly visible light photo-processes, have allowed for controllable generation of free radicals as well as the subsequent bond formations. The past five years have witnessed dramatic advances in exploring photo-induced catalytic asymmetric free radical reactions, and enormous potentials along this line are envisaged. This perspective gives a brief summary on the important advances in this field. Accordingly, the major advances are classified based on different radical species including α-amino/oxyl radicals, radicals generated from enones and its analogues, benzyl radicals, α-carbonyl radicals, polyhalogenated alkyl radicals and nitrogen radicals. Brief discussion of mechanism is presented whenever relevant.
2017, 75(1): 34-40
doi: 10.6023/A16090491
Abstract:
Taking advantages of the mild, clean and earth-abundant characters of visible light catalysis, we have invented a new reaction, namely cross-coupling hydrogen evolution (CCHE) reaction, for the construction of a series of C-C bond, C-X (heteroatom) bond, or X-X bond directly from two different C-H bonds, C-H and X-H bonds, or X-H and X-H bonds, respectively. In contrast to traditional strategies, this CCHE reaction avoids the use of any external oxidant and H2 is the sole product at ambient condition. In this contribution, we will highlight the development of CCHE reaction since the first report in 2013 to provide guidance for cleaner, safer, and more efficient, step-economic and atom-economic organic transformation.
Taking advantages of the mild, clean and earth-abundant characters of visible light catalysis, we have invented a new reaction, namely cross-coupling hydrogen evolution (CCHE) reaction, for the construction of a series of C-C bond, C-X (heteroatom) bond, or X-X bond directly from two different C-H bonds, C-H and X-H bonds, or X-H and X-H bonds, respectively. In contrast to traditional strategies, this CCHE reaction avoids the use of any external oxidant and H2 is the sole product at ambient condition. In this contribution, we will highlight the development of CCHE reaction since the first report in 2013 to provide guidance for cleaner, safer, and more efficient, step-economic and atom-economic organic transformation.
2017, 75(1): 41-48
doi: 10.6023/A16080416
Abstract:
The carboxyl and alkoxyl radicals generated from visible light photoredox reactions are important reaction intermediates in organic synthesis, which have witnessed conceivable progress recently. In this review, we focus on visible-light-induced photoredox methods to generate carboxyl radicals from carboxylate derivatives and carboxylates, as well as alkoxyl radicals from alcohol derivatives and alcohols, and briefly discuss their synthetic applications.
The carboxyl and alkoxyl radicals generated from visible light photoredox reactions are important reaction intermediates in organic synthesis, which have witnessed conceivable progress recently. In this review, we focus on visible-light-induced photoredox methods to generate carboxyl radicals from carboxylate derivatives and carboxylates, as well as alkoxyl radicals from alcohol derivatives and alcohols, and briefly discuss their synthetic applications.
2017, 75(1): 49-59
doi: 10.6023/A16090470
Abstract:
Many Ru (Ⅱ) complexes can undergo photoinduced ligand dissociation in aqueous solutions, and the formed aqua Ru (Ⅱ) species may bind to DNA covalently. This property has been applied to develop novel photoactivated chemotherapy (PACT) agents for cancer treatment in recent years. By finely tuning ligand structures and coordination configurations, PACT may realize highly selective and on-demand release of active species in cancer tissues, leading to an improved efficacy and diminished side effects. In this review, the progress in Ru (Ⅱ)-based PACT agents was fully discussed and a perspective for their future development was included.
Many Ru (Ⅱ) complexes can undergo photoinduced ligand dissociation in aqueous solutions, and the formed aqua Ru (Ⅱ) species may bind to DNA covalently. This property has been applied to develop novel photoactivated chemotherapy (PACT) agents for cancer treatment in recent years. By finely tuning ligand structures and coordination configurations, PACT may realize highly selective and on-demand release of active species in cancer tissues, leading to an improved efficacy and diminished side effects. In this review, the progress in Ru (Ⅱ)-based PACT agents was fully discussed and a perspective for their future development was included.
2017, 75(1): 60-65
doi: 10.6023/A16070375
Abstract:
Fluorinated compounds have gained much attention because of their unique electronegativity, metabolic stability and bioavailability, and thus, the synthesis of organofluorine compounds has found wide applications in pharmaceuticals, agrochemicals, and materials science. Among them, the incorporation of a difluoromethyl group (CF2) into organic compounds is of great concern in medicinal chemistry owing to its isosterism with the hydroxyl group. Therefore, the development of new difluoroalkylation methods has attracted great interest in synthetic organic chemistry. Visible light-driven photocatalysis as an eco-friendly and powerful theme has been widely utilized in organic synthesis. In particular, free radical fluorination is emerging as a powerful tool for C-F bond formation, especially under the catalysis of visible light. Recent progress on the visible light-promoted directing difluoroalkylation using ethyl bromodifluoroacetate provided an efficient approach to the target. Herein, we report a contribution towards visible light induced carbodifluoroalkylation of homopropargylic alcohols with the use of ethyl bromodifluoroacetate as a source of difluorinated moieties. This strategy provides a facile way to access functional-difluorinated alkenes through a tandem radical difluoroalkylation and 1, 4-aryl migration process. A representative procedure for this reaction is as following:An oven-dried Schlenk tube (10 mL) was equipped with a magnetic stir bar, homopropargylic alcohols (0.2 mmol), fac-Ir (ppy)3 (0.02 equiv., 0.004 mmol), 2-bromo-2, 2-difluoroacetate (2.5 equiv. 0.5 mmol), Na2HPO4 (2 equiv., 0.4 mmol). The flask was evacuated and backfilled with Ar for 3 times. 0.5 mL of dry DMA and 0.5 mL of dry DCE were added with syringe under Ar. The tube was placed at a distance (app. 5 cm) from 33 W fluorescent light bulb, and the resulting solution was stirred at ambient temperature under visible-light irradiation. After the reaction was finished, the mixture was then diluted with MTBE (20 mL×2) and water. The combined organic layers were dried over sodium sulfate and the solvent concentrated in vacuo and the residue was purified by chromatography on silica gel to afford the corresponding products.
Fluorinated compounds have gained much attention because of their unique electronegativity, metabolic stability and bioavailability, and thus, the synthesis of organofluorine compounds has found wide applications in pharmaceuticals, agrochemicals, and materials science. Among them, the incorporation of a difluoromethyl group (CF2) into organic compounds is of great concern in medicinal chemistry owing to its isosterism with the hydroxyl group. Therefore, the development of new difluoroalkylation methods has attracted great interest in synthetic organic chemistry. Visible light-driven photocatalysis as an eco-friendly and powerful theme has been widely utilized in organic synthesis. In particular, free radical fluorination is emerging as a powerful tool for C-F bond formation, especially under the catalysis of visible light. Recent progress on the visible light-promoted directing difluoroalkylation using ethyl bromodifluoroacetate provided an efficient approach to the target. Herein, we report a contribution towards visible light induced carbodifluoroalkylation of homopropargylic alcohols with the use of ethyl bromodifluoroacetate as a source of difluorinated moieties. This strategy provides a facile way to access functional-difluorinated alkenes through a tandem radical difluoroalkylation and 1, 4-aryl migration process. A representative procedure for this reaction is as following:An oven-dried Schlenk tube (10 mL) was equipped with a magnetic stir bar, homopropargylic alcohols (0.2 mmol), fac-Ir (ppy)3 (0.02 equiv., 0.004 mmol), 2-bromo-2, 2-difluoroacetate (2.5 equiv. 0.5 mmol), Na2HPO4 (2 equiv., 0.4 mmol). The flask was evacuated and backfilled with Ar for 3 times. 0.5 mL of dry DMA and 0.5 mL of dry DCE were added with syringe under Ar. The tube was placed at a distance (app. 5 cm) from 33 W fluorescent light bulb, and the resulting solution was stirred at ambient temperature under visible-light irradiation. After the reaction was finished, the mixture was then diluted with MTBE (20 mL×2) and water. The combined organic layers were dried over sodium sulfate and the solvent concentrated in vacuo and the residue was purified by chromatography on silica gel to afford the corresponding products.
2017, 75(1): 74-79
doi: 10.6023/A16090492
Abstract:
α-Arylated and α, α'-diarylated carbonyls are an important class of building blocks and widely found in biologically active natural and unnatural molecules. The most popular approach to access α-arylated and α, α'-diarylated carbonyls involves transition-metal-catalyzed cross-coupling reactions and metal-free coupling reactions, which always request harsh conditions or high catalytic loading. Visible-light photoredox catalysis, a novel and green catalytic strategy, has recently received increasing attention from chemists and been widely applied to organic synthesis in the past years. Inspired by the recent process of the visible light photocatalytic generation and exploration of α-keto acids as the precursor for acyl radical in decarboxylative cou-pling reactions and 1, 4-Michael addition reactions, we found that, however, expand their utilization in more complex systems, such as 1, 6-conjugate addition with electron deficient olefins, remains underdeveloped, particularly due to the difficult to design the appropriate substrate, and the harsh conditions often required for metal-catalyzed redox neutral decarboxylation. Here, we report a photoredox catalytic C-C bond formation reaction that enabled by visible-light. The versatility of this protocol has been portrayed by using a wide range of stable and easily accessible aromatic α-keto acids as well as p-QMs. This synthetic strategy also offers access to 24 kinds of different α-keto-α, α'-diarylated ketones in moderate to excellent yields under mild conditions. A representative procedure for the reaction is as follows:2-oxo-2-phenylacetic acid 1a (0.10 mmol), the p-QM (2, 6-di-tert-butyl-4-(4-methoxybenzylidene) cyclohexa-2, 5-dien-1-one) 2a (0.12 mmol), photocatalyst Ir[dF (CF3) PPy]2(dtbbpy) PF6 (0.001 mmol) and K2HPO4 (0.12 mmol) were dissolved in DCM (1 mL). Then, the resulting mixture was degassed and refilled with N2 via 'freeze-pump-thaw' procedure (3 times). After that, the solution was stirred at a distance of ca. 5 cm from a 36 W blue LEDs at room temperature for about 12 h with TLC monitoring. Upon completion of the reaction, the crude product was purified by flash chromatography on silica gel (hexane/ethyl acetate) to give the desired product 3.
α-Arylated and α, α'-diarylated carbonyls are an important class of building blocks and widely found in biologically active natural and unnatural molecules. The most popular approach to access α-arylated and α, α'-diarylated carbonyls involves transition-metal-catalyzed cross-coupling reactions and metal-free coupling reactions, which always request harsh conditions or high catalytic loading. Visible-light photoredox catalysis, a novel and green catalytic strategy, has recently received increasing attention from chemists and been widely applied to organic synthesis in the past years. Inspired by the recent process of the visible light photocatalytic generation and exploration of α-keto acids as the precursor for acyl radical in decarboxylative cou-pling reactions and 1, 4-Michael addition reactions, we found that, however, expand their utilization in more complex systems, such as 1, 6-conjugate addition with electron deficient olefins, remains underdeveloped, particularly due to the difficult to design the appropriate substrate, and the harsh conditions often required for metal-catalyzed redox neutral decarboxylation. Here, we report a photoredox catalytic C-C bond formation reaction that enabled by visible-light. The versatility of this protocol has been portrayed by using a wide range of stable and easily accessible aromatic α-keto acids as well as p-QMs. This synthetic strategy also offers access to 24 kinds of different α-keto-α, α'-diarylated ketones in moderate to excellent yields under mild conditions. A representative procedure for the reaction is as follows:2-oxo-2-phenylacetic acid 1a (0.10 mmol), the p-QM (2, 6-di-tert-butyl-4-(4-methoxybenzylidene) cyclohexa-2, 5-dien-1-one) 2a (0.12 mmol), photocatalyst Ir[dF (CF3) PPy]2(dtbbpy) PF6 (0.001 mmol) and K2HPO4 (0.12 mmol) were dissolved in DCM (1 mL). Then, the resulting mixture was degassed and refilled with N2 via 'freeze-pump-thaw' procedure (3 times). After that, the solution was stirred at a distance of ca. 5 cm from a 36 W blue LEDs at room temperature for about 12 h with TLC monitoring. Upon completion of the reaction, the crude product was purified by flash chromatography on silica gel (hexane/ethyl acetate) to give the desired product 3.
2017, 75(1): 80-85
doi: 10.6023/A16090496
Abstract:
In the past several years, visible light induced organic transformations via photoredox catalysis have attracted increasing attention from chemists, owing to their mild, environmentally benign and low cost characteristics. Photoredox catalysts including noble metal complexes as well as some organic dyes are often used to promote the transformations under visible light irradiation. However, most of the reactions were conducted in homogeneous system, which makes it difficult to recycle the catalysts for reuse. From a sustainable viewpoint, an ideal photocatalyst should be easily recoverable, reusable and free of precious metals. To this end, photoactive metal-organic frameworks (MOFs) demonstrate unique advantageous features working as novel heterogeneous photocatalytic systems, yet their utilization toward organic transformations promoted by visible light has been limited. Herein we designed and synthesized a benzothiadiazole functionalized TPDC ligand H21 (TPDC=terphenyl-4, 4''-dicarboxylic acid). Briefly, a Suzuki reaction of 4, 7-dibromo-2, 1, 3-benzothiadiazole with 4-(methoxycarbonyl) phenylboronic acid yielded methyl ester precursor, which was hydrolysed by KOH to get the ligand H21 in a high yield. Dimethyl-substituted TPDC H22, on account of its better solubility, was synthesized to replace the original TPDC for preparation of MOF UiO-68 framework. Due to the same length of the two ligands, the mix-and-match synthetic strategy was utilized to construct the benzothiadiazole functionalized UiO-68 topological framework (i.e. MOF UiO-68-S). UiO-68-S was synthesized by heating the mixture of ZrCl4 and a combination of ligands H21 and H22 (1:1 molar ratio) in N, N'-dimethylformamide (DMF) using HAc as an additive at 100℃ for 2 days. Powder X-ray diffraction (XRD) was em-ployed to confirm its crystalline nature and isostructural with the parent UiO-68 framework. Nitrogen sorption experiment at 77 K revealed a typical type I reversible isotherm with Brunauer-Emmett-Teller (BET) surface area up to 1135 m2·g-1, indicating its high porosity. Moreover, the MOF can serve as a highly active photocatalyst for visible light promoted aerobic oxidation reactions, including the selective oxygenation of sulfides and oxidative hydroxylation of arylboronic acids. In addition, UiO-68-S can be recycled at least 5 times without significant loss of catalytic activity and its framework is maintained following the catalytic reaction.
In the past several years, visible light induced organic transformations via photoredox catalysis have attracted increasing attention from chemists, owing to their mild, environmentally benign and low cost characteristics. Photoredox catalysts including noble metal complexes as well as some organic dyes are often used to promote the transformations under visible light irradiation. However, most of the reactions were conducted in homogeneous system, which makes it difficult to recycle the catalysts for reuse. From a sustainable viewpoint, an ideal photocatalyst should be easily recoverable, reusable and free of precious metals. To this end, photoactive metal-organic frameworks (MOFs) demonstrate unique advantageous features working as novel heterogeneous photocatalytic systems, yet their utilization toward organic transformations promoted by visible light has been limited. Herein we designed and synthesized a benzothiadiazole functionalized TPDC ligand H21 (TPDC=terphenyl-4, 4''-dicarboxylic acid). Briefly, a Suzuki reaction of 4, 7-dibromo-2, 1, 3-benzothiadiazole with 4-(methoxycarbonyl) phenylboronic acid yielded methyl ester precursor, which was hydrolysed by KOH to get the ligand H21 in a high yield. Dimethyl-substituted TPDC H22, on account of its better solubility, was synthesized to replace the original TPDC for preparation of MOF UiO-68 framework. Due to the same length of the two ligands, the mix-and-match synthetic strategy was utilized to construct the benzothiadiazole functionalized UiO-68 topological framework (i.e. MOF UiO-68-S). UiO-68-S was synthesized by heating the mixture of ZrCl4 and a combination of ligands H21 and H22 (1:1 molar ratio) in N, N'-dimethylformamide (DMF) using HAc as an additive at 100℃ for 2 days. Powder X-ray diffraction (XRD) was em-ployed to confirm its crystalline nature and isostructural with the parent UiO-68 framework. Nitrogen sorption experiment at 77 K revealed a typical type I reversible isotherm with Brunauer-Emmett-Teller (BET) surface area up to 1135 m2·g-1, indicating its high porosity. Moreover, the MOF can serve as a highly active photocatalyst for visible light promoted aerobic oxidation reactions, including the selective oxygenation of sulfides and oxidative hydroxylation of arylboronic acids. In addition, UiO-68-S can be recycled at least 5 times without significant loss of catalytic activity and its framework is maintained following the catalytic reaction.
2017, 75(1): 66-69
doi: 10.6023/A16070341
Abstract:
An approach for direct trifluoromethylation of internal olefins of α-oxoketene dithioacetals has been achieved by using Ru (bpy)3Cl2 as photocatalyst and Togni's reagent as trifluoromethylating agent under irradiation with visible light. Under a nitrogen atmosphere, a mixture of α-oxoketene dithioacetal (0.1 mmol), Togni's reagent (0.15 mmol), Ru (bpy)3Cl2 (0.005 mmol), and Na2CO3 (0.3 mmol) in DMSO (1 mL) was stirred at room temperature for 72 h under 5 W Blue LEDS, which led to the trifluoromethylated products in 40%~90% yield. This protocol provides an efficient and easy access to prepare trifluoromethylated dithioalkyl α-oxoketene acetals under mild conditions, and is highlighted by its operational simplicity and avoiding using toxic reagent. Furthermore, the gram-scale reaction of 1a suggested the potential application of this protocol in organic synthesis.
An approach for direct trifluoromethylation of internal olefins of α-oxoketene dithioacetals has been achieved by using Ru (bpy)3Cl2 as photocatalyst and Togni's reagent as trifluoromethylating agent under irradiation with visible light. Under a nitrogen atmosphere, a mixture of α-oxoketene dithioacetal (0.1 mmol), Togni's reagent (0.15 mmol), Ru (bpy)3Cl2 (0.005 mmol), and Na2CO3 (0.3 mmol) in DMSO (1 mL) was stirred at room temperature for 72 h under 5 W Blue LEDS, which led to the trifluoromethylated products in 40%~90% yield. This protocol provides an efficient and easy access to prepare trifluoromethylated dithioalkyl α-oxoketene acetals under mild conditions, and is highlighted by its operational simplicity and avoiding using toxic reagent. Furthermore, the gram-scale reaction of 1a suggested the potential application of this protocol in organic synthesis.
2017, 75(1): 70-73
doi: 10.6023/A16080407
Abstract:
A visible-light-induced photocatalytic aerobic dehydrogenation of 4-piperidones and 2, 3-dihydro-4-quinolones has been developed. By utilizing dicyanopyrazine-derived chromophore (DPZ) as the photocatalyst, the dehydrogenation could provide 2, 3-dihydro-4-pyridones and 4-quinolones with satisfactory results (up to 75% yield). The current methodology presents a direct, sustainable and highly atom-economic approach to access these valuable N-containing heterocycles.
A visible-light-induced photocatalytic aerobic dehydrogenation of 4-piperidones and 2, 3-dihydro-4-quinolones has been developed. By utilizing dicyanopyrazine-derived chromophore (DPZ) as the photocatalyst, the dehydrogenation could provide 2, 3-dihydro-4-pyridones and 4-quinolones with satisfactory results (up to 75% yield). The current methodology presents a direct, sustainable and highly atom-economic approach to access these valuable N-containing heterocycles.
2017, 75(1): 86-91
doi: 10.6023/A16070367
Abstract:
The 3, 4-dihydroisoquinolinones are a privileged class of heterocyclic motifs and widely found in numerous biologically active compounds. Thus, the development of more efficient and practical methods for their synthesis is highly desirable. Traditional methods are typically focused on transition-metal catalyzed C-H functionalization. Inspired by the recent process of the visible light photocatalytic generation and exploration of N-radicals in organic synthesis, our group in 2014 developed a visible light-induced photocatalytic strategy for direct conversion of the N-H bonds of β, γ-unsaturated hydrazones into N-centred radicals for the first time, and used them in intramolecular radical hydroamination, enabling efficient synthesis of 4, 5-dihydropyrazole derivatives. By employing suitable additives or changing reaction parameters, we also successfully achieved highly regioselective 6-endo N-radical cyclization and oxyamination reactions based on N-centred radicals, providing the valuable 1, 6-dihydropyradazines, pyrazolines, and pyridazines in good yields. In the hope of extending such N-radical-mediated heterocycle synthesis further, we reported a transition-metal free and visible light photocatalytic N-radical-based intramolecular hydroamination of benzamides. The reaction provides a practical and efficient approach to various biologically important 3, 4-dihydroisoquinolinones with generally high yields. Importantly, the continuous flow reaction could significantly shorten the reaction time and still give rise to satisfactory yield. The sunlight irradiation reaction and gram-scale reaction also highlighted the potential synthetic utility of this method. A general procedure for the reaction is as follows:EosinY Na (6.21 mg, 0.009 mmol), NaOH (14.4 mg, 0.36 mmol), amide 1 (0.3 mmol) were dissolved in MeOH (6.0 mL), then, the resulting mixture was degassed via a 'freeze-pump-thaw' procedure (3 times). After that, the resulting mixture was stirred at a distance of ca. 5 cm from 3 W blue LEDs (450~460 nm) at room temperature until the starting amides were consumed as monitored by TLC analysis. After concentration in vacuo, the reaction residue was purified by flash chromatography on silica gel[V(petroleum ether)/V(ethyl acetate)=5:1~2:1] directly to give the desired product.
The 3, 4-dihydroisoquinolinones are a privileged class of heterocyclic motifs and widely found in numerous biologically active compounds. Thus, the development of more efficient and practical methods for their synthesis is highly desirable. Traditional methods are typically focused on transition-metal catalyzed C-H functionalization. Inspired by the recent process of the visible light photocatalytic generation and exploration of N-radicals in organic synthesis, our group in 2014 developed a visible light-induced photocatalytic strategy for direct conversion of the N-H bonds of β, γ-unsaturated hydrazones into N-centred radicals for the first time, and used them in intramolecular radical hydroamination, enabling efficient synthesis of 4, 5-dihydropyrazole derivatives. By employing suitable additives or changing reaction parameters, we also successfully achieved highly regioselective 6-endo N-radical cyclization and oxyamination reactions based on N-centred radicals, providing the valuable 1, 6-dihydropyradazines, pyrazolines, and pyridazines in good yields. In the hope of extending such N-radical-mediated heterocycle synthesis further, we reported a transition-metal free and visible light photocatalytic N-radical-based intramolecular hydroamination of benzamides. The reaction provides a practical and efficient approach to various biologically important 3, 4-dihydroisoquinolinones with generally high yields. Importantly, the continuous flow reaction could significantly shorten the reaction time and still give rise to satisfactory yield. The sunlight irradiation reaction and gram-scale reaction also highlighted the potential synthetic utility of this method. A general procedure for the reaction is as follows:EosinY Na (6.21 mg, 0.009 mmol), NaOH (14.4 mg, 0.36 mmol), amide 1 (0.3 mmol) were dissolved in MeOH (6.0 mL), then, the resulting mixture was degassed via a 'freeze-pump-thaw' procedure (3 times). After that, the resulting mixture was stirred at a distance of ca. 5 cm from 3 W blue LEDs (450~460 nm) at room temperature until the starting amides were consumed as monitored by TLC analysis. After concentration in vacuo, the reaction residue was purified by flash chromatography on silica gel[V(petroleum ether)/V(ethyl acetate)=5:1~2:1] directly to give the desired product.
2017, 75(1): 92-98
doi: 10.6023/A16070364
Abstract:
Heating the toluene solution of 4, 4-dimethyl-4, 5-dihydro-3H-pyrazole (N2C5H10) and Fe3(CO)12 at reflux for 1 h produces diiron hexacarbonyls Fe2(N2C5H10)(CO)6 (1, νCO(CH2Cl2):2069, 2022, 1986 cm-1). Compound 1 exhibits 34 e- configuration, in which (N2C5H10)2- coordinates to diiron (FeIFeI) centers featuring a butterfly structure. To a solution of 1 in toluene was added one equiv. of decarbonyl agent Me3NO in MeCN, and the mixture was stirred at room temperature for 20 min. Then, one equiv. of monophosphine was added. After 3 h, the solvent was removed and the residue was extracted into 5 mL CH2Cl2. The product Fe2(N2C5H10)(CO)5(PR3) (PR3=PPh3, 2a; PCy3, 2b) was obtained as brown crystals by allowing a pentane layer to diffuse into the CH2Cl2 solution at -20℃. 31P NMR spectra exhibit a singlet at δ 67 for 2a and δ 70 for 2b in CH2Cl2, respectively. In IR spectra, the νCO bands for 2a were displayed at 2032, 1968, 1952, 1907 cm-1, which are compared to 2024, 1959, 1937, 1893 cm-1 for 2b. Photolysis the toluene solution of 1 in the presence of chelating diphosphine ligands such as dppe[dppe=1, 2-C2H4(PPh2)2] and dppbz[dppbz=1, 2-C6H4(PPh2)2] affords diiron diphosphine carbonyl compounds. For dppe, the product was Fe2(N2C5H10)(CO)4(μ-dppe) (3a, 31P NMR (CD2Cl2):δ 95, FT-IR (CH2Cl2, νCO):1984, 1940, 1925 and 1900 cm-1), in which dppe is bridging the two iron centers. For more rigid diphosphine ligand dppbz, X-ray crystallographic analysis reveals the structure of Fe2(N2C5H10)(μ-CO)(CO)4(dppbz)[3b, 31P NMR (CD2Cl2):δ 93]. In 3b, (N2C5H10)2- coordinates to diiron centers in a planar mode, and dppbz chelates at one Fe site by the replacement of one CO ligand. Compound 3b features a Fe-CO-Fe rotated structure with a bridging CO ligand between the two Fe centers. The νCO bands for 3b were displayed at 1990, 1947, 1919, 1895 cm-1. With such a rotated structure, compound 3b provides a new approach for synthetic models of Hred state of [FeFe]-H2ase. The CCDC number for 1, 2a, 2b, 3a and 3b are 1494954, 1494955, 1494956, 1494966 and 1494957. All the compounds were well characterized by NMR, IR spectroscopy and elemental analysis.
Heating the toluene solution of 4, 4-dimethyl-4, 5-dihydro-3H-pyrazole (N2C5H10) and Fe3(CO)12 at reflux for 1 h produces diiron hexacarbonyls Fe2(N2C5H10)(CO)6 (1, νCO(CH2Cl2):2069, 2022, 1986 cm-1). Compound 1 exhibits 34 e- configuration, in which (N2C5H10)2- coordinates to diiron (FeIFeI) centers featuring a butterfly structure. To a solution of 1 in toluene was added one equiv. of decarbonyl agent Me3NO in MeCN, and the mixture was stirred at room temperature for 20 min. Then, one equiv. of monophosphine was added. After 3 h, the solvent was removed and the residue was extracted into 5 mL CH2Cl2. The product Fe2(N2C5H10)(CO)5(PR3) (PR3=PPh3, 2a; PCy3, 2b) was obtained as brown crystals by allowing a pentane layer to diffuse into the CH2Cl2 solution at -20℃. 31P NMR spectra exhibit a singlet at δ 67 for 2a and δ 70 for 2b in CH2Cl2, respectively. In IR spectra, the νCO bands for 2a were displayed at 2032, 1968, 1952, 1907 cm-1, which are compared to 2024, 1959, 1937, 1893 cm-1 for 2b. Photolysis the toluene solution of 1 in the presence of chelating diphosphine ligands such as dppe[dppe=1, 2-C2H4(PPh2)2] and dppbz[dppbz=1, 2-C6H4(PPh2)2] affords diiron diphosphine carbonyl compounds. For dppe, the product was Fe2(N2C5H10)(CO)4(μ-dppe) (3a, 31P NMR (CD2Cl2):δ 95, FT-IR (CH2Cl2, νCO):1984, 1940, 1925 and 1900 cm-1), in which dppe is bridging the two iron centers. For more rigid diphosphine ligand dppbz, X-ray crystallographic analysis reveals the structure of Fe2(N2C5H10)(μ-CO)(CO)4(dppbz)[3b, 31P NMR (CD2Cl2):δ 93]. In 3b, (N2C5H10)2- coordinates to diiron centers in a planar mode, and dppbz chelates at one Fe site by the replacement of one CO ligand. Compound 3b features a Fe-CO-Fe rotated structure with a bridging CO ligand between the two Fe centers. The νCO bands for 3b were displayed at 1990, 1947, 1919, 1895 cm-1. With such a rotated structure, compound 3b provides a new approach for synthetic models of Hred state of [FeFe]-H2ase. The CCDC number for 1, 2a, 2b, 3a and 3b are 1494954, 1494955, 1494956, 1494966 and 1494957. All the compounds were well characterized by NMR, IR spectroscopy and elemental analysis.
2017, 75(1): 99-104
doi: 10.6023/A16100544
Abstract:
A protonated polyamidoamine (PAMAM) dendrimer of generation 2 with pyrenyl attached to its periphery (G2 PAMAM-PyH) was designed and synthesized. G2 PAMAM-Py was synthesized by a condensation of the terminal amino group of the PAMAM dendrimer and the aldehyde group of 1-pyrenecarboxaldehyde followed by a reduction of Schiff base through "one pot" reaction. G2 PAMAM-Py was further protonated by adding HCl, giving the target product G2 PAMAM-PyH. The structure of G2 PAMAM-PyH was characterized by NMR, FTIR, and MS. The functionalization extent of the peripheral amino groups of PAMAM by pyrenyl is 100% according to the 1H NMR and UV-visible spectra. The amphiphilic G2 PAMAM-PyH is soluble in water with a critical aggregation concentration of 3.3×10-7 mol·dm-3. Absorption, dynamic light scattering (DLS), and transmission electronic microscopy (TEM) studies demonstrate that G2 PAMAM-PyH exists as vesicle with a bilayer membrane and an average hydrodynamic diameter of ca. 184 nm in aqueous phase. G2 PAMAM-PyH in aqueous phase exhibits dual fluorescence, pyrenyl monomer and excimer emission. The pyrenyl monomer fluorescence increases slightly and the pyrenyl excimer emission decreases monotonically upon temperature raising from 1 to 70℃. Meanwhile, the fluorescence color changes from green (low temperature) to blue (high temperature). The monomer emission enhancement is mainly attributed to less formation of excimer when rising temperature. The fluorescence intensity ratio of pyrenyl excimer to pyrenyl monomer (I495 nm/I398 nm) changes with varying temperature recoverably, and the relationship between I495 nm/I398 nm and temperature can be expressed as I495 nm/I398 nm=28.23-0.68t+3.21×10-3t2+1.83×10-5t3. The accuracy for the measurement of the temperature is better than 0.9℃ in the temperature range of 1~70℃, facilitating in situ gradient temperature measurement. The temperature gradient of aqueous phase in a glass tube is investigated by using G2 PAMAM-PyH, which is consistent with the detection result by using a thermocouple meter. This study provides a potential strategy for developing fluorescent temperature sensing system.
A protonated polyamidoamine (PAMAM) dendrimer of generation 2 with pyrenyl attached to its periphery (G2 PAMAM-PyH) was designed and synthesized. G2 PAMAM-Py was synthesized by a condensation of the terminal amino group of the PAMAM dendrimer and the aldehyde group of 1-pyrenecarboxaldehyde followed by a reduction of Schiff base through "one pot" reaction. G2 PAMAM-Py was further protonated by adding HCl, giving the target product G2 PAMAM-PyH. The structure of G2 PAMAM-PyH was characterized by NMR, FTIR, and MS. The functionalization extent of the peripheral amino groups of PAMAM by pyrenyl is 100% according to the 1H NMR and UV-visible spectra. The amphiphilic G2 PAMAM-PyH is soluble in water with a critical aggregation concentration of 3.3×10-7 mol·dm-3. Absorption, dynamic light scattering (DLS), and transmission electronic microscopy (TEM) studies demonstrate that G2 PAMAM-PyH exists as vesicle with a bilayer membrane and an average hydrodynamic diameter of ca. 184 nm in aqueous phase. G2 PAMAM-PyH in aqueous phase exhibits dual fluorescence, pyrenyl monomer and excimer emission. The pyrenyl monomer fluorescence increases slightly and the pyrenyl excimer emission decreases monotonically upon temperature raising from 1 to 70℃. Meanwhile, the fluorescence color changes from green (low temperature) to blue (high temperature). The monomer emission enhancement is mainly attributed to less formation of excimer when rising temperature. The fluorescence intensity ratio of pyrenyl excimer to pyrenyl monomer (I495 nm/I398 nm) changes with varying temperature recoverably, and the relationship between I495 nm/I398 nm and temperature can be expressed as I495 nm/I398 nm=28.23-0.68t+3.21×10-3t2+1.83×10-5t3. The accuracy for the measurement of the temperature is better than 0.9℃ in the temperature range of 1~70℃, facilitating in situ gradient temperature measurement. The temperature gradient of aqueous phase in a glass tube is investigated by using G2 PAMAM-PyH, which is consistent with the detection result by using a thermocouple meter. This study provides a potential strategy for developing fluorescent temperature sensing system.
2017, 75(1): 105-109
doi: 10.6023/A16080412
Abstract:
The incorporation of fluorine atoms or fluorinated moieties into organic molecules can often lead to significant changes of their physical, chemical, or biological properties. Consequently, fluorinated organic molecules are widely used in areas of pharmaceuticals, agrochemicals and materials. Traditional approaches for the incorporation of fluorinated moieties into organic molecules include nucleophilic, electrophilic, and radical pathways. Among them, radical fluoroalkylations under visible-light photoredox catalysis have attracted much attention because of the mild reaction conditions and broad functional-group tolerance. In our previous work, the radical fluoroalkylation of isocyanides with fluorinated sulfones as the fluoroalkyl radical precursors via Rf-SO2Ar bond cleavage has been achieved under visible-light photoredox catalysis (Rong, J. et al. Angew. Chem., Int. Ed. 2016, 55, 2743). Herein, as a logical extension of our previous research, we report the radical fluoroalkylation of aryl alkenes with fluorinated sulfones as the practical fluoroalkyl radical precursors under visible-light photoredox catalysis. Various fluoroalkyl radicals, including trifluoromethyl (CF3), difluoromethyl (HCF2), 1, 1-difluoroethyl (CH3CF2) and (phenyl) difluoromethyl (PhCF2) radicals, can be incorporated into styrene derivatives via this method, delivering the oxyfluoroalkylation products in 46%~93% yields. Typical procedures for this reaction are given as follows:to a Schlenk tube were added 2-vinylnaphthalene (1a) (0.20 mmol, 30.8 mg, 1.0 equiv.), trifluoromethyl 2-benzo[d]thiazolyl sulfone (2b) (0.24 mmol, 64.1 mg, 1.2 equiv.), fac-Ir (ppy)3 (2.7 mg, 0.004 mmol, 2 mol%), H2O (0.5 mL), and acetone (4.5 mL) sequentially. The resulting mixture was degassed with a freeze-pump-thaw procedure (3 times) and irradiated by a 6 W blue LED for 12 h. After the reaction completed, the mixture was extracted with Et2O and dried over anhydrous MgSO4. The organic solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel by using a 10:1 (V/V) mixture of petroleum ether/EtOAc as an eluent to provide the hydroxytrifluoromethylation product 3a (31.2 mg, 65% yield).
The incorporation of fluorine atoms or fluorinated moieties into organic molecules can often lead to significant changes of their physical, chemical, or biological properties. Consequently, fluorinated organic molecules are widely used in areas of pharmaceuticals, agrochemicals and materials. Traditional approaches for the incorporation of fluorinated moieties into organic molecules include nucleophilic, electrophilic, and radical pathways. Among them, radical fluoroalkylations under visible-light photoredox catalysis have attracted much attention because of the mild reaction conditions and broad functional-group tolerance. In our previous work, the radical fluoroalkylation of isocyanides with fluorinated sulfones as the fluoroalkyl radical precursors via Rf-SO2Ar bond cleavage has been achieved under visible-light photoredox catalysis (Rong, J. et al. Angew. Chem., Int. Ed. 2016, 55, 2743). Herein, as a logical extension of our previous research, we report the radical fluoroalkylation of aryl alkenes with fluorinated sulfones as the practical fluoroalkyl radical precursors under visible-light photoredox catalysis. Various fluoroalkyl radicals, including trifluoromethyl (CF3), difluoromethyl (HCF2), 1, 1-difluoroethyl (CH3CF2) and (phenyl) difluoromethyl (PhCF2) radicals, can be incorporated into styrene derivatives via this method, delivering the oxyfluoroalkylation products in 46%~93% yields. Typical procedures for this reaction are given as follows:to a Schlenk tube were added 2-vinylnaphthalene (1a) (0.20 mmol, 30.8 mg, 1.0 equiv.), trifluoromethyl 2-benzo[d]thiazolyl sulfone (2b) (0.24 mmol, 64.1 mg, 1.2 equiv.), fac-Ir (ppy)3 (2.7 mg, 0.004 mmol, 2 mol%), H2O (0.5 mL), and acetone (4.5 mL) sequentially. The resulting mixture was degassed with a freeze-pump-thaw procedure (3 times) and irradiated by a 6 W blue LED for 12 h. After the reaction completed, the mixture was extracted with Et2O and dried over anhydrous MgSO4. The organic solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel by using a 10:1 (V/V) mixture of petroleum ether/EtOAc as an eluent to provide the hydroxytrifluoromethylation product 3a (31.2 mg, 65% yield).
2017, 75(1): 110-114
doi: 10.6023/A16080414
Abstract:
Visible-light photoredox catalysis, a novel and green catalytic strategy, has recently received increasing attention from chemists and been widely applied to organic synthesis in the past years. This catalytic strategy enables the generation of various reactive species under mild conditions without stoichiometric activation reagents and shows its significance for sustainable chemistry. α-Amino nitriles are highly versatile intermediates having extensive applications in organic synthesis and biological transformation. The oxidation of tertiary amines using stoichiometric oxidants followed by the nucleophilic addition reaction of the iminium intermediate by cyanide ion (CN-) represents a direct approach for their synthesis. However, the use of stoichiometric oxidants and the production of huge amounts of hazardous waste (i.e., CN-) is undesirable from environmental viewpoints. Here, we report a photoredox catalytic α-cyanation reaction of tertiary amines using cyanobenziodoxol as a stable and safe cyanide source. This protocol is favored for mild conditions, the avoidance of extra oxidant and highly toxic cyano anion, good functional tolerance as well as safe and simple operations. By doing so, a variety of α-amino nitriles are afforded in good to excellent yields. A sunlight-driven reaction and a gram-scale reaction further demonstrate the utility of this methodology. In addition, we also succeed to apply the same strategy to the decarboxylative cyanation of carboxylic acids, affording the nitriles in moderate yields. A possible mechanism was proposed on the basis of known literature and our previous reports. The representative procedure for the α-cyanation reaction of tertiary amines is as following:N-phenyl piperidine 1a (0.48 mmol), cyanobenziodoxol 2a (0.40 mmol), photocatalyst Ir[dF (CF3) PPy]2(dtbbpy) PF6 (0.008 mmol) and CsHCO3 (0.60 mmol) were dissolved in DCM (8 mL). Then, the resulting mixture was degassed via 'freeze-pump-thaw' procedure (3 times). After that, the solution was stirred at a distance of ca. 5 cm from a 7 W blue LEDs (450~460 nm) at room temperature for 16 h. Upon completion, the crude product was purified by flash chromatography on silica gel (petroleum ether/ethyl acetate 30:1~10:1) directly to give the desired product. The procedure for the decarboxylative cyanation of carboxylic acids is similar.
Visible-light photoredox catalysis, a novel and green catalytic strategy, has recently received increasing attention from chemists and been widely applied to organic synthesis in the past years. This catalytic strategy enables the generation of various reactive species under mild conditions without stoichiometric activation reagents and shows its significance for sustainable chemistry. α-Amino nitriles are highly versatile intermediates having extensive applications in organic synthesis and biological transformation. The oxidation of tertiary amines using stoichiometric oxidants followed by the nucleophilic addition reaction of the iminium intermediate by cyanide ion (CN-) represents a direct approach for their synthesis. However, the use of stoichiometric oxidants and the production of huge amounts of hazardous waste (i.e., CN-) is undesirable from environmental viewpoints. Here, we report a photoredox catalytic α-cyanation reaction of tertiary amines using cyanobenziodoxol as a stable and safe cyanide source. This protocol is favored for mild conditions, the avoidance of extra oxidant and highly toxic cyano anion, good functional tolerance as well as safe and simple operations. By doing so, a variety of α-amino nitriles are afforded in good to excellent yields. A sunlight-driven reaction and a gram-scale reaction further demonstrate the utility of this methodology. In addition, we also succeed to apply the same strategy to the decarboxylative cyanation of carboxylic acids, affording the nitriles in moderate yields. A possible mechanism was proposed on the basis of known literature and our previous reports. The representative procedure for the α-cyanation reaction of tertiary amines is as following:N-phenyl piperidine 1a (0.48 mmol), cyanobenziodoxol 2a (0.40 mmol), photocatalyst Ir[dF (CF3) PPy]2(dtbbpy) PF6 (0.008 mmol) and CsHCO3 (0.60 mmol) were dissolved in DCM (8 mL). Then, the resulting mixture was degassed via 'freeze-pump-thaw' procedure (3 times). After that, the solution was stirred at a distance of ca. 5 cm from a 7 W blue LEDs (450~460 nm) at room temperature for 16 h. Upon completion, the crude product was purified by flash chromatography on silica gel (petroleum ether/ethyl acetate 30:1~10:1) directly to give the desired product. The procedure for the decarboxylative cyanation of carboxylic acids is similar.
2017, 75(1): 115-118
doi: 10.6023/A16090480
Abstract:
A halogen-bond-promoted double radical isocyanide insertion of o-diisocyanoarenes with perfluoroalkyl bromides is reported, in which perfluoroalkyl bromides as halogen bond donors and organic bases as halogen bond acceptors. Fluoroalkyl radicals can be generated by a visible-light-induced single electron transfer (SET) process. Fluoroalkyl radicals are trapped by o-diisocyanoarenes to give 2-fluoroalkylated quinoxaline derivatives. These reactions could be carried out under mild conditions with good chemical yields and broad substrate scope. A broad range of fluoroalkyl bromides with different functionalities could undergo this reaction to give the corresponding quinoxaline derivatives in good yields. A variety of o-diisocyanides could be fluoroalkylated to give quinoxalines under our established conditions. The radical nature of this reaction was confirmed by electron paramagnetic resonance (EPR) experiments using tert-butyl-α-phenylnitrone (PBN) as a spin trap. When PBN was introduced into the reaction mixture, a spectrum signal attributed to the spin adduct C8F17-PBN appeared as a triplet of doublets. Without light and amine, almost no signal was observed. These phenomena strongly suggested that the perfluoroalkyl radical was the key intermediate and the generation of the intermediate heavily relied on the presence of light and amine. A series of deuteration experiments were performed and these results suggested that both the amine and solvent could serve as the hydrogen source and solvent was the major source.
A halogen-bond-promoted double radical isocyanide insertion of o-diisocyanoarenes with perfluoroalkyl bromides is reported, in which perfluoroalkyl bromides as halogen bond donors and organic bases as halogen bond acceptors. Fluoroalkyl radicals can be generated by a visible-light-induced single electron transfer (SET) process. Fluoroalkyl radicals are trapped by o-diisocyanoarenes to give 2-fluoroalkylated quinoxaline derivatives. These reactions could be carried out under mild conditions with good chemical yields and broad substrate scope. A broad range of fluoroalkyl bromides with different functionalities could undergo this reaction to give the corresponding quinoxaline derivatives in good yields. A variety of o-diisocyanides could be fluoroalkylated to give quinoxalines under our established conditions. The radical nature of this reaction was confirmed by electron paramagnetic resonance (EPR) experiments using tert-butyl-α-phenylnitrone (PBN) as a spin trap. When PBN was introduced into the reaction mixture, a spectrum signal attributed to the spin adduct C8F17-PBN appeared as a triplet of doublets. Without light and amine, almost no signal was observed. These phenomena strongly suggested that the perfluoroalkyl radical was the key intermediate and the generation of the intermediate heavily relied on the presence of light and amine. A series of deuteration experiments were performed and these results suggested that both the amine and solvent could serve as the hydrogen source and solvent was the major source.
2017, 75(1): 119-122
doi: 10.6023/A16080421
Abstract:
Pyridine derivatives play an important role in curing and controlling mites, bacteria, weed and so on. Pyrimidine derivatives exist in a number of bioactive natural products, and they have anti-allergy, anti-cancer, anti-inflammatory, insecticidal and some other properties. 3, 4-Disubstituted thiophenes not only are important units for the synthesis of natural products, but also serve as key components in some biologically active compounds and material chemistry. In modern society, we have the urgent demand for achieving our products atom economicly and environment-friendly. Under this background, "atom-economy" reactions have been drawing great attention from many chemists and they have got many exciting improvements since then. So, we want to make our own contributions to this area and the following are some of our preliminary results. Our method was based on synergistic application of eosin Y with nickel (Ⅱ) complex and an external oxidant-free oxidative dehydrogenation aromatization has been developed. At room temperature, Hantzsch 1, 4-dihydropyridines, 1, 4-dihydropyrimidines, 2, 5-dihydrothiophenes and 2, 5-dihydropyrroles were transformed into corresponding aromatic compounds in excellent yield under visible light irradiation via hydrogen evolution. We determined the hydrogen with GC-TCD using pure hydrogen as an external standard. It features very mild reaction conditions, high yields and excellent chemo-selectivity. In the previous reports, these transformations usually required higher temperatures and/or stronger oxidizing reagents, resulting in the generation of a large amount of by-products. In addition, the hydrogen evolution reactions were also compared with those of aerobic dehydrogenation. The results indicated that the dehydrogenation aromatizations of hantzsch 1, 4-dihydropyridines and 1, 4-dihydropyrimidine derivatives under the hydrogen evolution conditions proceeded in higher yields but very low conversions, while the reactions of 2, 5-dihydrothiophenes and 2, 5-dihydropyrroles gave higher conversions in the aerobic dehydrogenation conditions. So far, this is the first report using organic dye material combined with nickel (Ⅱ) complexes to achieve dihydrogen dehydrogenation aromatization of heterocyclic compounds.
Pyridine derivatives play an important role in curing and controlling mites, bacteria, weed and so on. Pyrimidine derivatives exist in a number of bioactive natural products, and they have anti-allergy, anti-cancer, anti-inflammatory, insecticidal and some other properties. 3, 4-Disubstituted thiophenes not only are important units for the synthesis of natural products, but also serve as key components in some biologically active compounds and material chemistry. In modern society, we have the urgent demand for achieving our products atom economicly and environment-friendly. Under this background, "atom-economy" reactions have been drawing great attention from many chemists and they have got many exciting improvements since then. So, we want to make our own contributions to this area and the following are some of our preliminary results. Our method was based on synergistic application of eosin Y with nickel (Ⅱ) complex and an external oxidant-free oxidative dehydrogenation aromatization has been developed. At room temperature, Hantzsch 1, 4-dihydropyridines, 1, 4-dihydropyrimidines, 2, 5-dihydrothiophenes and 2, 5-dihydropyrroles were transformed into corresponding aromatic compounds in excellent yield under visible light irradiation via hydrogen evolution. We determined the hydrogen with GC-TCD using pure hydrogen as an external standard. It features very mild reaction conditions, high yields and excellent chemo-selectivity. In the previous reports, these transformations usually required higher temperatures and/or stronger oxidizing reagents, resulting in the generation of a large amount of by-products. In addition, the hydrogen evolution reactions were also compared with those of aerobic dehydrogenation. The results indicated that the dehydrogenation aromatizations of hantzsch 1, 4-dihydropyridines and 1, 4-dihydropyrimidine derivatives under the hydrogen evolution conditions proceeded in higher yields but very low conversions, while the reactions of 2, 5-dihydrothiophenes and 2, 5-dihydropyrroles gave higher conversions in the aerobic dehydrogenation conditions. So far, this is the first report using organic dye material combined with nickel (Ⅱ) complexes to achieve dihydrogen dehydrogenation aromatization of heterocyclic compounds.
