Login In
2017 Volume 37 Issue 5
2017, 37(5): 1055-1068
doi: 10.6023/cjoc201702050
Abstract:
This mini-review focuses on the recent advances in the synthesis of organophosphorus compounds via cross coupling of P-H compounds with readily available starting materials, mainly including the reactions of terminal alkynes and heteroatom compounds (oxygen, sulfur or nitrogen-contained compounds) with P-H compounds forming sp-C-P, sp2-C-P, sp3-C-P, and P-Z bonds. Related reaction mechanisms are also discussed.
This mini-review focuses on the recent advances in the synthesis of organophosphorus compounds via cross coupling of P-H compounds with readily available starting materials, mainly including the reactions of terminal alkynes and heteroatom compounds (oxygen, sulfur or nitrogen-contained compounds) with P-H compounds forming sp-C-P, sp2-C-P, sp3-C-P, and P-Z bonds. Related reaction mechanisms are also discussed.
2017, 37(5): 1069-1087
doi: 10.6023/cjoc201702001
Abstract:
Chan-Evans-Lam reaction has been served as a powerful cross-coupling reaction in organic synthesis since its discovery in the 1990s owing to the feature of mild reaction conditions, functional group tolerance and open-flask chemistry. Up to now, it has been not only extensively utilized in carbon-heteroatom or carbon-carbon bonds formation, but also successfully applied to synthesize natural products and alkaloids. The new strategies of Chan-Evans-Lam reaction in organic synthesis as well as applications in total synthesis in recent five years are discussesed.
Chan-Evans-Lam reaction has been served as a powerful cross-coupling reaction in organic synthesis since its discovery in the 1990s owing to the feature of mild reaction conditions, functional group tolerance and open-flask chemistry. Up to now, it has been not only extensively utilized in carbon-heteroatom or carbon-carbon bonds formation, but also successfully applied to synthesize natural products and alkaloids. The new strategies of Chan-Evans-Lam reaction in organic synthesis as well as applications in total synthesis in recent five years are discussesed.
2017, 37(5): 1088-1098
doi: 10.6023/cjoc201702040
Abstract:
Recently, palladium-catalyzed alkyl-Heck reaction causes more attentions due to the wide application in the construction of C(sp3)-C(sp2). This review gives an up-to-date overview of alkyl-Heck reaction involving palladium radical intermediates, which are sorted in two categories of intramolecular reactions and intermolecular reactions. For most of these transformations, the plausible mechanisms are demonstrated in details. Clarification of these issues is the key point for understanding the palladium radical involved alkyl-Heck reactions and developing new high performance methodologies.
Recently, palladium-catalyzed alkyl-Heck reaction causes more attentions due to the wide application in the construction of C(sp3)-C(sp2). This review gives an up-to-date overview of alkyl-Heck reaction involving palladium radical intermediates, which are sorted in two categories of intramolecular reactions and intermolecular reactions. For most of these transformations, the plausible mechanisms are demonstrated in details. Clarification of these issues is the key point for understanding the palladium radical involved alkyl-Heck reactions and developing new high performance methodologies.
2017, 37(5): 1099-1110
doi: 10.6023/cjoc201702013
Abstract:
Asymmetric allylic alkylation reaction of 1, 3-dicarbonyl compounds is one of the most important methods for forming chiral carbon center. This review summarizes the progress on transition metal-catalyzed asymmetric allylic alkylation reaction of 1, 3-dicarbonyl compounds. Different allylating reagents such as allylic esters, allylic alcohols, allylic halides, olefins, allenes and others for the synthesis of α-allyl substituted 1, 3-dicarbonyl compounds are discussed.
Asymmetric allylic alkylation reaction of 1, 3-dicarbonyl compounds is one of the most important methods for forming chiral carbon center. This review summarizes the progress on transition metal-catalyzed asymmetric allylic alkylation reaction of 1, 3-dicarbonyl compounds. Different allylating reagents such as allylic esters, allylic alcohols, allylic halides, olefins, allenes and others for the synthesis of α-allyl substituted 1, 3-dicarbonyl compounds are discussed.
2017, 37(5): 1111-1116
doi: 10.6023/cjoc201702045
Abstract:
C-H bond functionalization is one of the hot spots in the research field of organic chemistry, and selective C-H activation is a challenging project. Among these reactions, organic solvent is normally used as reaction media. Using cheap, environmentally friendly water as reaction solvent would be in line with the requirements of "green chemistry" and low-carbon sustainable development. This paper reviews the recent progress of aqueous catalyzed C-H functionalization reactions, including hybridized sp-, sp2-, and sp3-C-H bonds.
C-H bond functionalization is one of the hot spots in the research field of organic chemistry, and selective C-H activation is a challenging project. Among these reactions, organic solvent is normally used as reaction media. Using cheap, environmentally friendly water as reaction solvent would be in line with the requirements of "green chemistry" and low-carbon sustainable development. This paper reviews the recent progress of aqueous catalyzed C-H functionalization reactions, including hybridized sp-, sp2-, and sp3-C-H bonds.
2017, 37(5): 1117-1126
doi: 10.6023/cjoc201702020
Abstract:
C-H bond functionalization has been one of the most important subject in chemistry. How to control the site selectivity of C-H bond is the key issue and remain challenge. Transition-metal-catalyzed organic tranformation of diazo compounds, such as X-H (X=O, N, S, etc.) insertion, cyclopropanation, cross-coupling reactions and C(sp3)-H functionalization, have been well established, whereas the C(sp2)-H functionalization using diazo compounds is less developed. This review will summarize the progress in transition-metal-catalyzed C(sp2)-H functionalization of arenes with diazo compounds. To realize the site selectivity, two strategies are utilized. One is directed C-H activation, which gives the ortho-selective C-H functionalization products. The other is undirected approach, which normally exhibits para-selectivity. In order to understand these reactions, the mechanisms for selected examples are also provided.
C-H bond functionalization has been one of the most important subject in chemistry. How to control the site selectivity of C-H bond is the key issue and remain challenge. Transition-metal-catalyzed organic tranformation of diazo compounds, such as X-H (X=O, N, S, etc.) insertion, cyclopropanation, cross-coupling reactions and C(sp3)-H functionalization, have been well established, whereas the C(sp2)-H functionalization using diazo compounds is less developed. This review will summarize the progress in transition-metal-catalyzed C(sp2)-H functionalization of arenes with diazo compounds. To realize the site selectivity, two strategies are utilized. One is directed C-H activation, which gives the ortho-selective C-H functionalization products. The other is undirected approach, which normally exhibits para-selectivity. In order to understand these reactions, the mechanisms for selected examples are also provided.
2017, 37(5): 1127-1138
doi: 10.6023/cjoc201610034
Abstract:
N-Alkylation of amines is a class of important organic reaction. The products of this reaction are related to the important technological fields including chemical, medical, pharmaceutical and defense. In recent years, the development and need of green catalytic synthesis technology make such C-N bond formation reaction via N-alkylation become one of the current research focuses of organic chemistry. Because water is the only by-product, the N-alkylation of amines with alcohols as alkylating agents is green, environmental, simple and reliable. However, the most of such reactions require a late transition metal catalyst. In this paper the progress in late transition metal-catalyzed N-alkylation reaction with alcohols as alkylating agents starting from various aliphatic, aromatic and heterocyclic aromatic amines in recent years is reviewed. Various homogeneous and heterogeneous catalytic systems as well as the substrate application scope of each method involved in this reaction are mainly introduced. The expectation and development direction about this N-alkylation in future are suggested.
N-Alkylation of amines is a class of important organic reaction. The products of this reaction are related to the important technological fields including chemical, medical, pharmaceutical and defense. In recent years, the development and need of green catalytic synthesis technology make such C-N bond formation reaction via N-alkylation become one of the current research focuses of organic chemistry. Because water is the only by-product, the N-alkylation of amines with alcohols as alkylating agents is green, environmental, simple and reliable. However, the most of such reactions require a late transition metal catalyst. In this paper the progress in late transition metal-catalyzed N-alkylation reaction with alcohols as alkylating agents starting from various aliphatic, aromatic and heterocyclic aromatic amines in recent years is reviewed. Various homogeneous and heterogeneous catalytic systems as well as the substrate application scope of each method involved in this reaction are mainly introduced. The expectation and development direction about this N-alkylation in future are suggested.
2017, 37(5): 1139-1159
doi: 10.6023/cjoc201612011
Abstract:
Polylactides have received considerable attention in recent years due to their outstanding properties such as biocompatibility, biodegradability, and renewability. In particular, the studies on ring opening polymerization (ROP) of lactides in stereoselective manner catalyzed by chiral organometallic complexes have been regarded as one of the most significant fields in the synthesis of polylactides. The important advances in the ROP of lactides catalyzed by chiral organometallic complexes are reviewed in this article.
Polylactides have received considerable attention in recent years due to their outstanding properties such as biocompatibility, biodegradability, and renewability. In particular, the studies on ring opening polymerization (ROP) of lactides in stereoselective manner catalyzed by chiral organometallic complexes have been regarded as one of the most significant fields in the synthesis of polylactides. The important advances in the ROP of lactides catalyzed by chiral organometallic complexes are reviewed in this article.
2017, 37(5): 1160-1164
doi: 10.6023/cjoc201702036
Abstract:
A novel iron catalyzed hydroarylation, methylarylation, and diarylation of styrenes to form unsymmetrical 1, 1-diarylalkanes with electron rich anisole and 1, 3, 5-trimethoxybenzene under mild conditions have been developed. Benzoyl peroxide is used as an oxidant for hydroarylation, whereas in the case of methylarylation and diarylation the oxidant tert-butyl peracetate is used.
A novel iron catalyzed hydroarylation, methylarylation, and diarylation of styrenes to form unsymmetrical 1, 1-diarylalkanes with electron rich anisole and 1, 3, 5-trimethoxybenzene under mild conditions have been developed. Benzoyl peroxide is used as an oxidant for hydroarylation, whereas in the case of methylarylation and diarylation the oxidant tert-butyl peracetate is used.
2017, 37(5): 1165-1172
doi: 10.6023/cjoc201701043
Abstract:
The first rhodium-catalyzed stereospecific intermolecular [3+2] cycloaddition reaction of vinylaziridines with ynamides was realized. The salient features of the transformation include broad substrate scope, mild reaction condition, and simple operation. Moreover, the chirality of vinylaziridines can be completely transferred to the cycloadducts, representing an atom-economic and enantiospecific protocol for the construction of valuable 2-amino pyrroline derivatives.
The first rhodium-catalyzed stereospecific intermolecular [3+2] cycloaddition reaction of vinylaziridines with ynamides was realized. The salient features of the transformation include broad substrate scope, mild reaction condition, and simple operation. Moreover, the chirality of vinylaziridines can be completely transferred to the cycloadducts, representing an atom-economic and enantiospecific protocol for the construction of valuable 2-amino pyrroline derivatives.
2017, 37(5): 1173-1180
doi: 10.6023/cjoc201702042
Abstract:
An efficient copper-catalyzed oxysulfenylation of alkenoic acids with benzenethiols via radical pathway was developed. The reactions are easy to be conducted under mild conditions and form a broad range of sulfenylated lactones.
An efficient copper-catalyzed oxysulfenylation of alkenoic acids with benzenethiols via radical pathway was developed. The reactions are easy to be conducted under mild conditions and form a broad range of sulfenylated lactones.
2017, 37(5): 1181-1188
doi: 10.6023/cjoc201703003
Abstract:
Carbolong complexes are a new type of metalla-aromatic compounds with novel skeleton and interesting properties, which could be used as potential interesting materials. However, most of them do not have reactive organic functional groups, which hinder their applications as functional materials via chemical modifications. Olefinic group is a reactive functional group that can be used for polymerization or click reaction and so on. In this work, the synthesis of carbolong complexes attached an olefinic group, which could be used to prepare carbolong-containing materials, is reported based on their reactivity.
Carbolong complexes are a new type of metalla-aromatic compounds with novel skeleton and interesting properties, which could be used as potential interesting materials. However, most of them do not have reactive organic functional groups, which hinder their applications as functional materials via chemical modifications. Olefinic group is a reactive functional group that can be used for polymerization or click reaction and so on. In this work, the synthesis of carbolong complexes attached an olefinic group, which could be used to prepare carbolong-containing materials, is reported based on their reactivity.
2017, 37(5): 1189-1197
doi: 10.6023/cjoc201703024
Abstract:
The direct reductive cyanation of N-benzyl-4-benzyloxy-5-hydroxymethyl-2-pyrrolidinone (3a), a lactam bearing a free hydroxyl group, has been achieved with the LiAlH4/KCN combination. The reaction afforded 2, 5-trans-2-cyano-5-hydroxylmethyl-4-benzyloxy-pyrrolidine (5a) and its cis-diastereomer 5b in a ratio of 69:31 with a combined yield of 63%. The observed 2, 5-trans-stereoselectivity is suggested to be resulted from both stereoelectronic effect and allylic 1, 3-strain between the hydroxymethyl group at C(5) and the incoming cyanide anion on the presumed Δ-1 pyrrolinium ion intermediate. The subsequent hydrolysis of the cyano group of the diastereomeric mixture 5a/5b (trans:cis=69:31) under basic conditions afforded the corresponding 5-hydroxymethyl-4-benzyloxyproline with 2, 5-cis-diastereomer as the major diastereomer (trans:cis=10:90). This result implies that a synthetically useful epimerization at C(2) has occurred concomitantly. This unexpected result afforded a concise and highly stereoselective synthesis of 2, 5-cis-(-)-N-methyl-2-epi-bulgecinine.
The direct reductive cyanation of N-benzyl-4-benzyloxy-5-hydroxymethyl-2-pyrrolidinone (3a), a lactam bearing a free hydroxyl group, has been achieved with the LiAlH4/KCN combination. The reaction afforded 2, 5-trans-2-cyano-5-hydroxylmethyl-4-benzyloxy-pyrrolidine (5a) and its cis-diastereomer 5b in a ratio of 69:31 with a combined yield of 63%. The observed 2, 5-trans-stereoselectivity is suggested to be resulted from both stereoelectronic effect and allylic 1, 3-strain between the hydroxymethyl group at C(5) and the incoming cyanide anion on the presumed Δ-1 pyrrolinium ion intermediate. The subsequent hydrolysis of the cyano group of the diastereomeric mixture 5a/5b (trans:cis=69:31) under basic conditions afforded the corresponding 5-hydroxymethyl-4-benzyloxyproline with 2, 5-cis-diastereomer as the major diastereomer (trans:cis=10:90). This result implies that a synthetically useful epimerization at C(2) has occurred concomitantly. This unexpected result afforded a concise and highly stereoselective synthesis of 2, 5-cis-(-)-N-methyl-2-epi-bulgecinine.
2017, 37(5): 1205-1212
doi: 10.6023/cjoc201701051
Abstract:
A copper iodide catalyzed reaction of aldehydes and t-butyl hydroperoxide (TBHP) was developed for the synthesis of peresters in the presence of bipyridine ligand under mild and neat conditions. The addition of bipyridine ligand increased the catalytic activities of copper catalyst significantly and triggered the reaction. The reaction showed good tolerance to various substrates, and good to excellent yields were obtained. Furthermore, a one-pot synthesis of allylic esters was also achieved by the addition of cyclohexene to the reaction mixture under neat condition at relative lower temperature.
A copper iodide catalyzed reaction of aldehydes and t-butyl hydroperoxide (TBHP) was developed for the synthesis of peresters in the presence of bipyridine ligand under mild and neat conditions. The addition of bipyridine ligand increased the catalytic activities of copper catalyst significantly and triggered the reaction. The reaction showed good tolerance to various substrates, and good to excellent yields were obtained. Furthermore, a one-pot synthesis of allylic esters was also achieved by the addition of cyclohexene to the reaction mixture under neat condition at relative lower temperature.
2017, 37(5): 1231-1236
doi: 10.6023/cjoc201701033
Abstract:
Density functional theory (DFT) calculations are employed to study the mechanism of alkaline earth metal catalyzed hydroboration of carbodiimides. Our theoretical study revealed that the active catalytic species is a hydridemagnesium complex when magnesium is used as catalyst. The catalytic cycle starts with a C=N bond insertion into Mg-H bond followed by a B-N bond formation. A hydride transfer from boron to magnesium regenerates the active catalytic species and yields the hydroboration product. This process is considered to be the rate-determining step. Moreover, the mechanism of calcium or strontium catalyzed corresponding reactions was also studied theoretically. Alternatively, DFT calculations showed that the active catalytic species is amide-metal complex, which could be generated by the carbodiimide insertion into metal-hydride bond. In this catalytic cycle, amide-metal complex reacts with borane to form a B-N bond. After the coordination of another molecular carbodiimide, a concerted hydride transfer takes place from boron to carbon, which yields the final product and regenerates the active species amide-metal. The different reaction pathway with calcium or strontium catalyzed corresponding reactions could be attributed to that the radius of calcium or strontium is larger than that of magnesium significantly. Thus, those two metals would be coordinated with an extra carbodiimide molecule, which is the precursor for the concerted hydride transfer. The DFT calculations showed that the activation free energy for the rate-determining step with calcium or strontium catalyst is much lower than that with magnesium catalyst. Therefore, a mild reaction condition might be found with calcium or strontium as catalyst for corresponding reactions.
Density functional theory (DFT) calculations are employed to study the mechanism of alkaline earth metal catalyzed hydroboration of carbodiimides. Our theoretical study revealed that the active catalytic species is a hydridemagnesium complex when magnesium is used as catalyst. The catalytic cycle starts with a C=N bond insertion into Mg-H bond followed by a B-N bond formation. A hydride transfer from boron to magnesium regenerates the active catalytic species and yields the hydroboration product. This process is considered to be the rate-determining step. Moreover, the mechanism of calcium or strontium catalyzed corresponding reactions was also studied theoretically. Alternatively, DFT calculations showed that the active catalytic species is amide-metal complex, which could be generated by the carbodiimide insertion into metal-hydride bond. In this catalytic cycle, amide-metal complex reacts with borane to form a B-N bond. After the coordination of another molecular carbodiimide, a concerted hydride transfer takes place from boron to carbon, which yields the final product and regenerates the active species amide-metal. The different reaction pathway with calcium or strontium catalyzed corresponding reactions could be attributed to that the radius of calcium or strontium is larger than that of magnesium significantly. Thus, those two metals would be coordinated with an extra carbodiimide molecule, which is the precursor for the concerted hydride transfer. The DFT calculations showed that the activation free energy for the rate-determining step with calcium or strontium catalyst is much lower than that with magnesium catalyst. Therefore, a mild reaction condition might be found with calcium or strontium as catalyst for corresponding reactions.
2017, 37(5): 1237-1245
doi: 10.6023/cjoc201701034
Abstract:
The first cobalt-catalyzed benzylation of aminoquinolines on C(5) position has been developed. The C(sp2)-H/ C(sp3)-H cross-coupling of quinolineamides and butylated hydroxytoluene (BHT) could yield the desired products via bidentate-chelation assistance. Under the optimal reaction condition of Co(OAc)2·4H2O (20 mol%), AgTFA (2.0 equiv.), 120 ℃ for 12 h, the reaction is compatible with a wide range of quinoline substrates. This protocol provides a facile access to the benzyl substituted quinolines.
The first cobalt-catalyzed benzylation of aminoquinolines on C(5) position has been developed. The C(sp2)-H/ C(sp3)-H cross-coupling of quinolineamides and butylated hydroxytoluene (BHT) could yield the desired products via bidentate-chelation assistance. Under the optimal reaction condition of Co(OAc)2·4H2O (20 mol%), AgTFA (2.0 equiv.), 120 ℃ for 12 h, the reaction is compatible with a wide range of quinoline substrates. This protocol provides a facile access to the benzyl substituted quinolines.
2017, 37(5): 1246-1251
doi: 10.6023/cjoc201612040
Abstract:
Amide is one of the most important functional groups in nature. Besides the classical synthetic method by using activated acid with amine, several other transition metal-catalyzed protocols have been developed. Aryl nitriles have also attracted substantial attentions as herbicides, natural products, etc. Traditional methods towards aryl nitriles include Sandmeyer and Rosenmund von Braun reaction. In addition of these methods, researchers have explored various kinds of toxic "CN" sources. In continuation of our previous work on copper catalyzed C-CN bond cleavage and C-N formation reactions, herein our recent work of combination of copper-catalyzed amidation of benzyl cyanide and cyanation of aryl iodides by using N, N-dimethyl formamide (DMF) as amide source is reported. A representative procedure for this reaction is as following: benzyl cyanide (1 mmol), iodobenzene (1 mmol), DMF (2 mL), TsOH (1 mmol), Cu2O (0.2 mmol), 1, 10-phenanthroline (0.4 mmol) were added into a 10 mL of Schlenk tube. The mixture was stirred at 130 ℃ under O2 atmosphere for 12 h. The reaction mixture was then cooled down to room temperature, quenched with water, and extracted with ethyl acetate. The organic layer was then dried over anhydrous MgSO4, and the solvent was removed in vacuo. The residue was finally purified by column chromatography on silica gel using petroleum ether-ethyl acetate mixture as eluent. A variety of N, N-dimethyl benzamides and benzonitriles were obtained in yields up to 85% and 75%, respectively.
Amide is one of the most important functional groups in nature. Besides the classical synthetic method by using activated acid with amine, several other transition metal-catalyzed protocols have been developed. Aryl nitriles have also attracted substantial attentions as herbicides, natural products, etc. Traditional methods towards aryl nitriles include Sandmeyer and Rosenmund von Braun reaction. In addition of these methods, researchers have explored various kinds of toxic "CN" sources. In continuation of our previous work on copper catalyzed C-CN bond cleavage and C-N formation reactions, herein our recent work of combination of copper-catalyzed amidation of benzyl cyanide and cyanation of aryl iodides by using N, N-dimethyl formamide (DMF) as amide source is reported. A representative procedure for this reaction is as following: benzyl cyanide (1 mmol), iodobenzene (1 mmol), DMF (2 mL), TsOH (1 mmol), Cu2O (0.2 mmol), 1, 10-phenanthroline (0.4 mmol) were added into a 10 mL of Schlenk tube. The mixture was stirred at 130 ℃ under O2 atmosphere for 12 h. The reaction mixture was then cooled down to room temperature, quenched with water, and extracted with ethyl acetate. The organic layer was then dried over anhydrous MgSO4, and the solvent was removed in vacuo. The residue was finally purified by column chromatography on silica gel using petroleum ether-ethyl acetate mixture as eluent. A variety of N, N-dimethyl benzamides and benzonitriles were obtained in yields up to 85% and 75%, respectively.
2017, 37(5): 1258-1265
doi: 10.6023/cjoc201610039
Abstract:
Four imidazolium precursors for the N-heterocyclic carbenes (NHCs) with a hydroxyl functionalized four-mem-bered heterocyclic side arm were synthesized and characterized by IR, XRD and NMR spectroscopies. The corresponding NHC ligands thus generated in situ from these imidazolium precursors in the presence of base such as KOH, together with PdCl2(CH3CN)2, exhibited excellent catalytic activity in Suzuki-Miyaura cross-coupling reactions for the synthesis of a range of biaryl compounds. The reactions could be conducted in the mixed solvent of tert-butyl alcohol/water (V:V=1:1) at room temperature with the advantages of mild conditions, high efficiency as well as environmental friendliness. In addition, although in minor amount, the mixed catalyst system containing imidazolium salts, PdCl2(CH3CN)2 (0.1%) and CuI (1%) exhibited excellent catalytic activity in Sonogashira coupling reaction. In particular, the combination system of PdCl2/imidazolium salt 3b has been shown to be higher catalytically active for both coupling reactions.
Four imidazolium precursors for the N-heterocyclic carbenes (NHCs) with a hydroxyl functionalized four-mem-bered heterocyclic side arm were synthesized and characterized by IR, XRD and NMR spectroscopies. The corresponding NHC ligands thus generated in situ from these imidazolium precursors in the presence of base such as KOH, together with PdCl2(CH3CN)2, exhibited excellent catalytic activity in Suzuki-Miyaura cross-coupling reactions for the synthesis of a range of biaryl compounds. The reactions could be conducted in the mixed solvent of tert-butyl alcohol/water (V:V=1:1) at room temperature with the advantages of mild conditions, high efficiency as well as environmental friendliness. In addition, although in minor amount, the mixed catalyst system containing imidazolium salts, PdCl2(CH3CN)2 (0.1%) and CuI (1%) exhibited excellent catalytic activity in Sonogashira coupling reaction. In particular, the combination system of PdCl2/imidazolium salt 3b has been shown to be higher catalytically active for both coupling reactions.
2017, 37(5): 1198-1204
doi: 10.6023/cjoc201702004
Abstract:
A general strategy for the syntheses of 4, 4', 6, 6'-substituted-2, 2'-bipyridines starting from aromatic aldehyde is described. A series of sodium cryptates and two europium cryptates [Eu⊂bpy·bpy·bpy]·2Cl·Br (bpy=6, 6'-dimethylene-2, 2'-bipyridine-4, 4'-dimethylester) (23) and [Eu⊂bpy1·bpy1·bpy2]·2Cl·Br (bpy1=6, 6'-dimethylene-2, 2'-bipyridine-4, 4'-dicarboxylic acid, bpy2=6, 6'-dimethylene-2, 2'-bipyridine-4, 4'-diformylethylenediamine) (24), were synthesized from these compounds. Sodium cryptates have been confirmed by 1H NMR, 13C NMR and high resolution mass spectrum (HRMS). The structure of europium cryptate 23 was confirmed by X-ray diffraction (XRD) and HRMS. The photoluminescence (PL) spectra, decay curve and the absolute quantum efficiency (η) of 23 are presented. 23 can be efficiently excited by near-UV light and presents a bright red luminescence with the lifetime (τ) of 0.32 ms and the η of 70%. It is suggested that 23 is expected to be a potential efficient phosphor for lighting and display.
A general strategy for the syntheses of 4, 4', 6, 6'-substituted-2, 2'-bipyridines starting from aromatic aldehyde is described. A series of sodium cryptates and two europium cryptates [Eu⊂bpy·bpy·bpy]·2Cl·Br (bpy=6, 6'-dimethylene-2, 2'-bipyridine-4, 4'-dimethylester) (23) and [Eu⊂bpy1·bpy1·bpy2]·2Cl·Br (bpy1=6, 6'-dimethylene-2, 2'-bipyridine-4, 4'-dicarboxylic acid, bpy2=6, 6'-dimethylene-2, 2'-bipyridine-4, 4'-diformylethylenediamine) (24), were synthesized from these compounds. Sodium cryptates have been confirmed by 1H NMR, 13C NMR and high resolution mass spectrum (HRMS). The structure of europium cryptate 23 was confirmed by X-ray diffraction (XRD) and HRMS. The photoluminescence (PL) spectra, decay curve and the absolute quantum efficiency (η) of 23 are presented. 23 can be efficiently excited by near-UV light and presents a bright red luminescence with the lifetime (τ) of 0.32 ms and the η of 70%. It is suggested that 23 is expected to be a potential efficient phosphor for lighting and display.
2017, 37(5): 1213-1219
doi: 10.6023/cjoc201612052
Abstract:
Homocoupling of oxazole/thiazole via palladium-catalyzed C-H bond activation using oxone as an oxidant has been achieved in moderate to excellent yields with good functional group tolerance. No other additive or ligand was employed in this efficient reaction. Comparing to our previously reported homocoupling of oxazole/thiazole, the absence of stoichiometric silver oxidant renders this reaction more environment-benign and cost-effective. A preliminary mechanism involving a PdⅡ/PdⅣ catalytic cycle is also proposed. Further exploration of this environmental-benign oxidant on other categories of coupling reactions, as well as applications of this revised homocoupling to structural modification of oxazole/thiazole-containing natural products, are undergoing in our lab.
Homocoupling of oxazole/thiazole via palladium-catalyzed C-H bond activation using oxone as an oxidant has been achieved in moderate to excellent yields with good functional group tolerance. No other additive or ligand was employed in this efficient reaction. Comparing to our previously reported homocoupling of oxazole/thiazole, the absence of stoichiometric silver oxidant renders this reaction more environment-benign and cost-effective. A preliminary mechanism involving a PdⅡ/PdⅣ catalytic cycle is also proposed. Further exploration of this environmental-benign oxidant on other categories of coupling reactions, as well as applications of this revised homocoupling to structural modification of oxazole/thiazole-containing natural products, are undergoing in our lab.
Aminolysis of Esters Using Quaternary Ammonium Salts as Amine Sources via Twice C-N Bond Activations
2017, 37(5): 1220-1230
doi: 10.6023/cjoc201612014
Abstract:
Catalyzed by supported palladium nanoparticles, an aminolysis reaction between various aryl esters and quaternary ammonium salts via twice C-N bond activations has been developed for selectively synthesis of amides. The Pd/γ-Al2O3 catalyst exhibited an excellent catalytic activity and reusability of at least five recycles in air for the reaction. The experiment results indicated that the first C-N cleavage of quaternary ammonium salt affords the tertiary amine and halohydrocarbon, and the second C-N cleavage proceeds via the formation of an iminium intermediate.
Catalyzed by supported palladium nanoparticles, an aminolysis reaction between various aryl esters and quaternary ammonium salts via twice C-N bond activations has been developed for selectively synthesis of amides. The Pd/γ-Al2O3 catalyst exhibited an excellent catalytic activity and reusability of at least five recycles in air for the reaction. The experiment results indicated that the first C-N cleavage of quaternary ammonium salt affords the tertiary amine and halohydrocarbon, and the second C-N cleavage proceeds via the formation of an iminium intermediate.
2017, 37(5): 1252-1257
doi: 10.6023/cjoc201701024
Abstract:
A simple, efficient and eco-friendly "one-pot" method for the convenient synthesis of imidazo-fused heterocycles has been developed. The reaction was catalyzed by CeCl3·7H2O in ethanol under 60 ℃ via Groebke-Blackburn-Bienayme (GBB) reaction of aldehydes, aminoazines and isocyanides. This method has many advantages of a wide range of substrates, short reaction time and easy purification. In addition, we conducted a comparative study of LaCl3·7H2O with CeCl3·7H2O on their catalytic effect under the same reaction conditions, and found that CeCl3·7H2O was comparable to LaCl3·7H2O as catalyst in GBB reaction.
A simple, efficient and eco-friendly "one-pot" method for the convenient synthesis of imidazo-fused heterocycles has been developed. The reaction was catalyzed by CeCl3·7H2O in ethanol under 60 ℃ via Groebke-Blackburn-Bienayme (GBB) reaction of aldehydes, aminoazines and isocyanides. This method has many advantages of a wide range of substrates, short reaction time and easy purification. In addition, we conducted a comparative study of LaCl3·7H2O with CeCl3·7H2O on their catalytic effect under the same reaction conditions, and found that CeCl3·7H2O was comparable to LaCl3·7H2O as catalyst in GBB reaction.
2017, 37(5): 1266-1272
doi: 10.6023/cjoc201612049
Abstract:
Functionalized 6-arylsalicylate substructures occur in a variety of pharmacologically relevant natural products and bioactive compounds. Especially 6-arylsubstituted salicylates, as a key pharmacophore of anti-resistant acetohydroxyacid synthase (AHAS) inhibitors have played a lead role in combatting the weed-resistance issues. Previously, we have explored two new methods to synthesize position-6 aryl substituted salicylic acid fragment. However, these two methods failed to introduce various substituents into salicylic acid. Here an efficient method for the synthesis of 6-substituted salicylates is described via a microwave-promoted Suzuki cross-coupling. Due to the obvious advantages of this method, such as a wide range of substrates, smooth and rapid reaction and moderate to excellent yields, this protocol could be utilized to synthesize more anti-resistant AHAS inhibitors.
Functionalized 6-arylsalicylate substructures occur in a variety of pharmacologically relevant natural products and bioactive compounds. Especially 6-arylsubstituted salicylates, as a key pharmacophore of anti-resistant acetohydroxyacid synthase (AHAS) inhibitors have played a lead role in combatting the weed-resistance issues. Previously, we have explored two new methods to synthesize position-6 aryl substituted salicylic acid fragment. However, these two methods failed to introduce various substituents into salicylic acid. Here an efficient method for the synthesis of 6-substituted salicylates is described via a microwave-promoted Suzuki cross-coupling. Due to the obvious advantages of this method, such as a wide range of substrates, smooth and rapid reaction and moderate to excellent yields, this protocol could be utilized to synthesize more anti-resistant AHAS inhibitors.
2017, 37(5): 1273-1277
doi: 10.6023/cjoc201612015
Abstract:
A Cu-catalyzed protocol for the cyanation of aryl iodides by using acetonitrile as the "CN" source has been developed, in which the Cu(cat.)/2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPO)/Si system shows good reactivity and generality. Both electron-rich and electron-deficient functional groups can be tolerated in this system.
A Cu-catalyzed protocol for the cyanation of aryl iodides by using acetonitrile as the "CN" source has been developed, in which the Cu(cat.)/2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPO)/Si system shows good reactivity and generality. Both electron-rich and electron-deficient functional groups can be tolerated in this system.
2017, 37(5): 1278-1283
doi: 10.6023/cjoc201702031
Abstract:
Convenient and efficient protocol for isomerization of allylbenzenes into corresponding β-methylstyrenes has been developed. Different acids, solvents and catalysts have been investigated. Pd(TFA)2 and TsOH·H2O as catalysts in dichloromethane at room temperature under air for 12 h were selected as standard conditions for exploring the substrate scope. Allylbenzenes containing electron-donating groups and electron-withdrawing groups were working under the optimized condition, and β-methylstyrene products were obtained in the yields of 65%~90%. The reaction mechanism was proposed according to the deuterated experiment.
Convenient and efficient protocol for isomerization of allylbenzenes into corresponding β-methylstyrenes has been developed. Different acids, solvents and catalysts have been investigated. Pd(TFA)2 and TsOH·H2O as catalysts in dichloromethane at room temperature under air for 12 h were selected as standard conditions for exploring the substrate scope. Allylbenzenes containing electron-donating groups and electron-withdrawing groups were working under the optimized condition, and β-methylstyrene products were obtained in the yields of 65%~90%. The reaction mechanism was proposed according to the deuterated experiment.
2017, 37(5): 1300-1305
doi: 10.6023/cjoc201611035
Abstract:
The reactions of L1Li [L1=HC(CMeNAr)2, Ar=2, 6-iPr2C6H3] with Me2SnCl2, and L2Li [L2=HC(CMeNAr')2, Ar'=2, 6-Et2C6H3] with Me3SnCl in a molar ratio of 1:1 were carried out at room temperature and acquired two new compounds, N(Ar)=C(Me)CH=C(NHAr)CH2SnMe2Cl·C7H8 (1) and [N(Ar')C(Me)=CHC(=NAr')CH2SnMe2]2·CH2Cl2 (2), respectively. Different from regular nitrogen-metal-nitrogen bonds generated by the reactions of β-diketiminato ligands with metal halides, uncommon nitrogen-tin-carbon bonds in compounds 1 and 2 were obtained by Sn-N bond cleavage and concomitant Sn-C bond formation due to the Lewis acidity of SnMe3 and SnMe2Cl group. Compound 2 is a rare tin dimer with two resonant structures. Two compounds have been confirmed by 1H NMR, 13C NMR, elemental analysis, and single crystal X-ray structural analysis. Through the comparison of compounds 1 and 2, the formation mechanism of dimer 2 has been investigated.
The reactions of L1Li [L1=HC(CMeNAr)2, Ar=2, 6-iPr2C6H3] with Me2SnCl2, and L2Li [L2=HC(CMeNAr')2, Ar'=2, 6-Et2C6H3] with Me3SnCl in a molar ratio of 1:1 were carried out at room temperature and acquired two new compounds, N(Ar)=C(Me)CH=C(NHAr)CH2SnMe2Cl·C7H8 (1) and [N(Ar')C(Me)=CHC(=NAr')CH2SnMe2]2·CH2Cl2 (2), respectively. Different from regular nitrogen-metal-nitrogen bonds generated by the reactions of β-diketiminato ligands with metal halides, uncommon nitrogen-tin-carbon bonds in compounds 1 and 2 were obtained by Sn-N bond cleavage and concomitant Sn-C bond formation due to the Lewis acidity of SnMe3 and SnMe2Cl group. Compound 2 is a rare tin dimer with two resonant structures. Two compounds have been confirmed by 1H NMR, 13C NMR, elemental analysis, and single crystal X-ray structural analysis. Through the comparison of compounds 1 and 2, the formation mechanism of dimer 2 has been investigated.
2017, 37(5): 1284-1289
doi: 10.6023/cjoc201701052
Abstract:
In order to study the effect of the benzyl benzene ring on the catalytic behavior of binuclear metallocene, the binuclear metallocene [μ, μ-1, 4-(CH2)2(C6H4)] [(η5-C5H5)TiCl2(η5-(C6H5)C(Me)2(C5H3)]2 [(TiBz)2] is synthesized and characterized by 1H NMR, 13C NMR, mass spectra and elemental analysis. When combined with methylaluminoxane (MAO), the (TiBz)2/MAO system catalyzed ethylene polymerization and the polymer with C(4) branch were obtained. It is suggested that the C(4) branch is from the ethylene trimerization by the weak effect between the benzyl and center metal. The (TiBz)2/MAO system also showed great ability for ethylene copolymerization with 1-hexene and the incorporation of 1-hexene in polymer reached up to 13.7 mol%. The 13C NMR result of polymer showed that the polymer contained alternatively copolymerized HEHE fragment and the possible mechanism is presented for explaining the special catalytic behavior. It is the weak effect between the benzyl and center metal that led to the alternative insertion of ethylene and 1-hexene, and the narrow molecular weight distribution (PDI=2.23) meant that there could be a great synergistic effect between the two activate center metals in the polymerization process, which greatly increased the copolymerization capability.
In order to study the effect of the benzyl benzene ring on the catalytic behavior of binuclear metallocene, the binuclear metallocene [μ, μ-1, 4-(CH2)2(C6H4)] [(η5-C5H5)TiCl2(η5-(C6H5)C(Me)2(C5H3)]2 [(TiBz)2] is synthesized and characterized by 1H NMR, 13C NMR, mass spectra and elemental analysis. When combined with methylaluminoxane (MAO), the (TiBz)2/MAO system catalyzed ethylene polymerization and the polymer with C(4) branch were obtained. It is suggested that the C(4) branch is from the ethylene trimerization by the weak effect between the benzyl and center metal. The (TiBz)2/MAO system also showed great ability for ethylene copolymerization with 1-hexene and the incorporation of 1-hexene in polymer reached up to 13.7 mol%. The 13C NMR result of polymer showed that the polymer contained alternatively copolymerized HEHE fragment and the possible mechanism is presented for explaining the special catalytic behavior. It is the weak effect between the benzyl and center metal that led to the alternative insertion of ethylene and 1-hexene, and the narrow molecular weight distribution (PDI=2.23) meant that there could be a great synergistic effect between the two activate center metals in the polymerization process, which greatly increased the copolymerization capability.
Synthesis of 6-Aryl Phenanthridines via Iron-Catalyzed sp2-C-H Bond Amination/Aromatization Reaction
2017, 37(5): 1290-1294
doi: 10.6023/cjoc201701054
Abstract:
With FeCl2 as a catalyst and Selectfluor as an oxidant, an efficient and highly selective synthesis of 6-aryl phenanthridines in one-pot manner has been achieved via an intramolecular sp2-C-H bond amination/aromatization of N-(biphenyl-2-yl(aryl)methyl)benzenesulfonamide derivatives. The optimized reaction conditions were established through systematic investigations of solvents, temperature, catalysts, oxidants and their dosages in the reaction. The present reaction has advantages of simple operation, easy availability of starting materials, the use of inexpensive and low-toxic iron catalyst, and good compatibility of substrates.
With FeCl2 as a catalyst and Selectfluor as an oxidant, an efficient and highly selective synthesis of 6-aryl phenanthridines in one-pot manner has been achieved via an intramolecular sp2-C-H bond amination/aromatization of N-(biphenyl-2-yl(aryl)methyl)benzenesulfonamide derivatives. The optimized reaction conditions were established through systematic investigations of solvents, temperature, catalysts, oxidants and their dosages in the reaction. The present reaction has advantages of simple operation, easy availability of starting materials, the use of inexpensive and low-toxic iron catalyst, and good compatibility of substrates.
2017, 37(5): 1295-1299
doi: 10.6023/cjoc201702043
Abstract:
As one of the most abundant metals on earth, iron is cheap and low toxicity. Herein we reported the asymmetric transfer hydrogenation of (ATH) ketones catalyzed by the system generated in situ from chiral multidentate aminophosphine ligand (R, R, R, R)-PN4H6 and Fe3(CO)12. The effects of temperature and additive on the ATH of propiophenone were examined. After optimizing the reaction conditions, we applied the catalytic system to the ATH of various aromatic ketones, obtaining the corresponding optical active alcohols with high enantioselectivities (up to 96% ee).
As one of the most abundant metals on earth, iron is cheap and low toxicity. Herein we reported the asymmetric transfer hydrogenation of (ATH) ketones catalyzed by the system generated in situ from chiral multidentate aminophosphine ligand (R, R, R, R)-PN4H6 and Fe3(CO)12. The effects of temperature and additive on the ATH of propiophenone were examined. After optimizing the reaction conditions, we applied the catalytic system to the ATH of various aromatic ketones, obtaining the corresponding optical active alcohols with high enantioselectivities (up to 96% ee).
