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2019 Volume 30 Issue 8
2019, 30(8): 1461-1462
doi: 10.1016/j.cclet.2019.07.005
Abstract:
2019, 30(8): 1463-1467
doi: 10.1016/j.cclet.2019.05.026
Abstract:
Owing to their inexpensive and environmentally friendly properties, iron-based catalysts have been actively investigated for new organic reactions. In this account, we summarized our recent results on iron-catalyzed cross-coupling reactions and homo-coupling reactions. With iron-based catalysts, we constructed diverse carbon-carbon bonds, i.e., C(sp2)-C(sp3), C(sp3)-C(sp3), C(sp3)-C(sp2) and C(sp2)-C(sp2) bonds. In order to demonstrate the usefulness of our iron protocol, we also carried out these reactions on gram-scale reactions, leading to good yields
Owing to their inexpensive and environmentally friendly properties, iron-based catalysts have been actively investigated for new organic reactions. In this account, we summarized our recent results on iron-catalyzed cross-coupling reactions and homo-coupling reactions. With iron-based catalysts, we constructed diverse carbon-carbon bonds, i.e., C(sp2)-C(sp3), C(sp3)-C(sp3), C(sp3)-C(sp2) and C(sp2)-C(sp2) bonds. In order to demonstrate the usefulness of our iron protocol, we also carried out these reactions on gram-scale reactions, leading to good yields
2019, 30(8): 1468-1480
doi: 10.1016/j.cclet.2019.07.004
Abstract:
In 2015, a new antimicrobial peptide agent was discovered, termed teixobactin. Over the past few years, the structure-activity relationship of teixobactin has been extensively studied. Here, the updated studies have been summarized to provide structure-activity relationship established to date. It can be seen that position 1, 2, 5 and 6 of teixobactin are not tolerant of diversion from the native amino acids. In positions 7 and 11, native amino acids give the highest activity but there is tolerance for other amino acids. Positions 3, 4, 9 and 10 are very tolerant of substitution while maintaining good potency and a broad activity spectrum. Activity does not depend on absolute stereochemistry, but on the relative stereochemistry and positions 1, 4, 5, and 8 must contain D-amino acids. The ring and tail structure are necessary for activity, macrolactone and lactam rings are both acceptable. Some teixobactin analogues show greater activity than native teixobactin. All conducted animal studies show positive results with no animal deaths.
In 2015, a new antimicrobial peptide agent was discovered, termed teixobactin. Over the past few years, the structure-activity relationship of teixobactin has been extensively studied. Here, the updated studies have been summarized to provide structure-activity relationship established to date. It can be seen that position 1, 2, 5 and 6 of teixobactin are not tolerant of diversion from the native amino acids. In positions 7 and 11, native amino acids give the highest activity but there is tolerance for other amino acids. Positions 3, 4, 9 and 10 are very tolerant of substitution while maintaining good potency and a broad activity spectrum. Activity does not depend on absolute stereochemistry, but on the relative stereochemistry and positions 1, 4, 5, and 8 must contain D-amino acids. The ring and tail structure are necessary for activity, macrolactone and lactam rings are both acceptable. Some teixobactin analogues show greater activity than native teixobactin. All conducted animal studies show positive results with no animal deaths.
2019, 30(8): 1481-1487
doi: 10.1016/j.cclet.2019.04.008
Abstract:
In this review, the recent development in transition metal catalyzed cross coupling of nitroarenes was highlighted. Firstly, development of transition metal catalyzed cross coupling was simply introduced. After presenting the advantages of nitroarenes, transition metal catalyzed cross coupling using nitroarenes as electrophilic coupling partners was classified and introduced in detail. Based on different chemical bonds such as C–O, C–S, C–C and C–N bonds constructed, different kinds cross coupling of nitroarenes would be highlighted and the plausible reaction mechanism would be presented if available.
In this review, the recent development in transition metal catalyzed cross coupling of nitroarenes was highlighted. Firstly, development of transition metal catalyzed cross coupling was simply introduced. After presenting the advantages of nitroarenes, transition metal catalyzed cross coupling using nitroarenes as electrophilic coupling partners was classified and introduced in detail. Based on different chemical bonds such as C–O, C–S, C–C and C–N bonds constructed, different kinds cross coupling of nitroarenes would be highlighted and the plausible reaction mechanism would be presented if available.
2019, 30(8): 1488-1494
doi: 10.1016/j.cclet.2019.04.073
Abstract:
During the last decade, photo-catalysis is emerging as a powerful tool in synthetic organic chemistry. This mini-review summarizes the recent advances of photo-promoted organic transformations under transition metal-free conditions in the absence of conventional photo-sensitizers.
During the last decade, photo-catalysis is emerging as a powerful tool in synthetic organic chemistry. This mini-review summarizes the recent advances of photo-promoted organic transformations under transition metal-free conditions in the absence of conventional photo-sensitizers.
2019, 30(8): 1495-1502
doi: 10.1016/j.cclet.2019.04.027
Abstract:
Transition-metal-catalyzed C–H activation reaction has proven to be a powerful and efficient tool for the formation of diverse C–C and C–X bond and construction of functional complex molecules. From the viewpoint of sustainable chemistry, the first-row transition metals, such as Mn, Fe, Co, Ni and Cu, have been recognized as cheap, environmentally friendly and reactively effective catalysts for a number of C–H functionalization reactions. However, compared with the commonly used alkenes and alkynes in the first-row transition-metal-catalyzed C–H activations, considerable achievements have just been made by the use of structurally unique and reactively rich allenes as coupling partners in recent years. This review summarizes the recent progress of the first-row transition-metal-catalyzed C–H activations with allenes.
Transition-metal-catalyzed C–H activation reaction has proven to be a powerful and efficient tool for the formation of diverse C–C and C–X bond and construction of functional complex molecules. From the viewpoint of sustainable chemistry, the first-row transition metals, such as Mn, Fe, Co, Ni and Cu, have been recognized as cheap, environmentally friendly and reactively effective catalysts for a number of C–H functionalization reactions. However, compared with the commonly used alkenes and alkynes in the first-row transition-metal-catalyzed C–H activations, considerable achievements have just been made by the use of structurally unique and reactively rich allenes as coupling partners in recent years. This review summarizes the recent progress of the first-row transition-metal-catalyzed C–H activations with allenes.
2019, 30(8): 1503-1505
doi: 10.1016/j.cclet.2019.03.033
Abstract:
In this paper, we report the concise total syntheses of three botryane sesquiterpenoids: dehydrobotrydienal, dehydrobotrydienol, and 10-oxodehydrodihydrobotrydial. The key transformations include tandem Co-tetramethylthiourea-catalyzed Pauson-Khand and 6π-electrocyclization reactions to forge the tricyclic core structure of the botryanes, and further oxidative aromatization and oxidation to complete the total syntheses.
In this paper, we report the concise total syntheses of three botryane sesquiterpenoids: dehydrobotrydienal, dehydrobotrydienol, and 10-oxodehydrodihydrobotrydial. The key transformations include tandem Co-tetramethylthiourea-catalyzed Pauson-Khand and 6π-electrocyclization reactions to forge the tricyclic core structure of the botryanes, and further oxidative aromatization and oxidation to complete the total syntheses.
2019, 30(8): 1506-1508
doi: 10.1016/j.cclet.2019.04.013
Abstract:
A novel ketone-functionalized aromatic saddle consisting of 72 sp2 carbon atoms is successfully synthesized and unambiguously identified with X-ray crystallography. It can, in principle, be used as a building block for synthesis of negatively curved carbon nanobelts and for a bottom-up approach to negatively curved carbon allotropes.
A novel ketone-functionalized aromatic saddle consisting of 72 sp2 carbon atoms is successfully synthesized and unambiguously identified with X-ray crystallography. It can, in principle, be used as a building block for synthesis of negatively curved carbon nanobelts and for a bottom-up approach to negatively curved carbon allotropes.
2019, 30(8): 1509-1511
doi: 10.1016/j.cclet.2019.04.023
Abstract:
An electrochemical vicinal heterodifunctionalization of olefins for the synthesis of β-oxysulfones is described. With suitable choice of the conditions, including current, electrodes, and electrolyte, this oxidation reaction proceeded efficiently in an undivided cell without the use of a stoichiometric chemical oxidant. In addition to the previously established synthesis of β-hydroxysulfones in the presence of water, minor modification of this protocol by using either external alcohol nucleophiles or internal carboxylic acid nucleophile also led to the synthesis of β-alkoxysulfones, and β-sulfonyl lactones.
An electrochemical vicinal heterodifunctionalization of olefins for the synthesis of β-oxysulfones is described. With suitable choice of the conditions, including current, electrodes, and electrolyte, this oxidation reaction proceeded efficiently in an undivided cell without the use of a stoichiometric chemical oxidant. In addition to the previously established synthesis of β-hydroxysulfones in the presence of water, minor modification of this protocol by using either external alcohol nucleophiles or internal carboxylic acid nucleophile also led to the synthesis of β-alkoxysulfones, and β-sulfonyl lactones.
2019, 30(8): 1512-1514
doi: 10.1016/j.cclet.2019.04.028
Abstract:
A Pd-catalyzed asymmetric decarboxylative [4 + 2] cycloaddition of 3-nitroindoles and vinyl benzoxazinanones is developed through a dearomatization approach. The reaction provides an efficient protocol for constructing a series of chiral tetrahydro-5H-indolo[2, 3-b]quinolines in high yields and with excellent diastereo- and enantioselectivities.
A Pd-catalyzed asymmetric decarboxylative [4 + 2] cycloaddition of 3-nitroindoles and vinyl benzoxazinanones is developed through a dearomatization approach. The reaction provides an efficient protocol for constructing a series of chiral tetrahydro-5H-indolo[2, 3-b]quinolines in high yields and with excellent diastereo- and enantioselectivities.
2019, 30(8): 1515-1518
doi: 10.1016/j.cclet.2019.03.036
Abstract:
A facile and highly efficient approach for selective O-difluoromethylation of 1, 3-diones by recently developed bench-stable S-(difluoromethyl)sulfonium salt was described. And a broad range of difluoromthyl enol ethers were readily accessed in good to excellent yields under mild reaction conditions. Mechanistic studies revealed that the O-difluoromethylation reaction proceeds mainly via a difluorocarbene pathway.
A facile and highly efficient approach for selective O-difluoromethylation of 1, 3-diones by recently developed bench-stable S-(difluoromethyl)sulfonium salt was described. And a broad range of difluoromthyl enol ethers were readily accessed in good to excellent yields under mild reaction conditions. Mechanistic studies revealed that the O-difluoromethylation reaction proceeds mainly via a difluorocarbene pathway.
2019, 30(8): 1519-1522
doi: 10.1016/j.cclet.2019.04.042
Abstract:
α, β-Alkynyl ketoesters were introduced to the enantioselective Henry reaction (nitroaldol condensation) with nitromethane catalyzed by tartaric acid derived chiral iminophosphoranes. As such, a variety of optically active β-nitro-substituted tertiary alcohols bearing alkyne moieties were obtained in good to excellent yields (42%-99%) and moderate to good level of enantiomeric excess (up to 87% ee).
α, β-Alkynyl ketoesters were introduced to the enantioselective Henry reaction (nitroaldol condensation) with nitromethane catalyzed by tartaric acid derived chiral iminophosphoranes. As such, a variety of optically active β-nitro-substituted tertiary alcohols bearing alkyne moieties were obtained in good to excellent yields (42%-99%) and moderate to good level of enantiomeric excess (up to 87% ee).
2019, 30(8): 1523-1526
doi: 10.1016/j.cclet.2019.04.051
Abstract:
Furans bearing epoxy enolsilane units via a tether that incorporates a nitrogen heteroatom, undergo intramolecular (4 + 3) cycloadditions to generate bis-heteroatomic polycyclic adducts having piperidine moieties in their frameworks. The cycloadducts, ultimately derived from furfural, a renewal chemical feedstock, are obtained with up to 4:1 dr and with ee retained from the epoxide.
Furans bearing epoxy enolsilane units via a tether that incorporates a nitrogen heteroatom, undergo intramolecular (4 + 3) cycloadditions to generate bis-heteroatomic polycyclic adducts having piperidine moieties in their frameworks. The cycloadducts, ultimately derived from furfural, a renewal chemical feedstock, are obtained with up to 4:1 dr and with ee retained from the epoxide.
2019, 30(8): 1527-1529
doi: 10.1016/j.cclet.2019.04.043
Abstract:
A four-step synthesis of methyl 6-formyl-2-hydroxy-4-methoxy-3-(3-methylbut-2-en-1-yl)benzoate (11) that can be used as building block for a facile synthesis of cajaninstilbene acid and its derivatives is reported. The synthesis of cajaninstilbene acid was accomplished in six steps with an overall yield of 20% starting from commercial materials by a synthesis whose key steps are TiCl4-mediated [3 + 3] cyclization and McMurry coupling.
A four-step synthesis of methyl 6-formyl-2-hydroxy-4-methoxy-3-(3-methylbut-2-en-1-yl)benzoate (11) that can be used as building block for a facile synthesis of cajaninstilbene acid and its derivatives is reported. The synthesis of cajaninstilbene acid was accomplished in six steps with an overall yield of 20% starting from commercial materials by a synthesis whose key steps are TiCl4-mediated [3 + 3] cyclization and McMurry coupling.
2019, 30(8): 1530-1532
doi: 10.1016/j.cclet.2019.04.034
Abstract:
How long a C-C bond can be? A question has long fascinated chemists. This work reports an example of extraordinary long C-C bond distance of 1.990(4) Å observed in single-crystal X-ray structure of 1, 2-(NHMes)2-o-carborane (2; Mes=2, 4, 6-trimethylphenyl). DFT calculations show that hyperconjugation of lone pairs of the nitrogen atoms into the empty σ* orbital of the cage C-C bond is the origin of the bond elongation. Such hyperconjugation can be suppressed if the two nitrogen atoms in 2 are linked to a Lewis acidic germanium (Ⅱ) center.
How long a C-C bond can be? A question has long fascinated chemists. This work reports an example of extraordinary long C-C bond distance of 1.990(4) Å observed in single-crystal X-ray structure of 1, 2-(NHMes)2-o-carborane (2; Mes=2, 4, 6-trimethylphenyl). DFT calculations show that hyperconjugation of lone pairs of the nitrogen atoms into the empty σ* orbital of the cage C-C bond is the origin of the bond elongation. Such hyperconjugation can be suppressed if the two nitrogen atoms in 2 are linked to a Lewis acidic germanium (Ⅱ) center.
2019, 30(8): 1533-1537
doi: 10.1016/j.cclet.2019.06.014
Abstract:
An efficient and novel methodology to access phenolic glycosides has been established by using coppermediated coupling reaction of aryl boronic acids with hemiacetals. The reaction takes place normally in the presence of Cu(OAc)2 (1.0 equiv.) and pyridine (2.0 equiv.) at 40℃. This protocol distinguishes itself by wide substrate scope, operational simplicity and giving rise to a myriad of phenolic glycosides in good to excellent yields.
An efficient and novel methodology to access phenolic glycosides has been established by using coppermediated coupling reaction of aryl boronic acids with hemiacetals. The reaction takes place normally in the presence of Cu(OAc)2 (1.0 equiv.) and pyridine (2.0 equiv.) at 40℃. This protocol distinguishes itself by wide substrate scope, operational simplicity and giving rise to a myriad of phenolic glycosides in good to excellent yields.
2019, 30(8): 1538-1540
doi: 10.1016/j.cclet.2019.06.049
Abstract:
The AC bicyclic skeleton of daphniyunnine B with the required 3 stereocenters (C4, C5 and C8) was accomplished in a concise route which featured two Claisen-type rearrangement reactions to construct the required vicinal all carbon quaternary stereocenters (C5 and C8) and an intramolecular iodocyclization reaction to assemble the cis-confused bicyclic lactam.
The AC bicyclic skeleton of daphniyunnine B with the required 3 stereocenters (C4, C5 and C8) was accomplished in a concise route which featured two Claisen-type rearrangement reactions to construct the required vicinal all carbon quaternary stereocenters (C5 and C8) and an intramolecular iodocyclization reaction to assemble the cis-confused bicyclic lactam.
2019, 30(8): 1541-1544
doi: 10.1016/j.cclet.2019.07.001
Abstract:
A mild and efficient nBu4NBr-mediated oxidative cycloaromatization to prepare β-carbolines from readily available tryptophans and aldehydes is described. The reaction is practical and allows the synthesis of β-carbolines on gram-scale. Some of products crystallized from the reaction mixture and were easily removed by filtration, obviating the need for chromatographic separation.
A mild and efficient nBu4NBr-mediated oxidative cycloaromatization to prepare β-carbolines from readily available tryptophans and aldehydes is described. The reaction is practical and allows the synthesis of β-carbolines on gram-scale. Some of products crystallized from the reaction mixture and were easily removed by filtration, obviating the need for chromatographic separation.
