2019 Volume 30 Issue 8

Professor Henry N.C. Wong, extraordinary synthetic chemist and great mentor
2019, 30(8): 1461-1462  doi: 10.1016/j.cclet.2019.07.005
[Abstract](203) [FullText HTML] [PDF 1184KB](3)
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Recent advances on iron-catalyzed coupling reactions involving organolithium reagents
Zhong Zhuliang , Peng Xiao-Shui , Wong Henry N. C.
2019, 30(8): 1463-1467  doi: 10.1016/j.cclet.2019.05.026
[Abstract](214) [FullText HTML] [PDF 6648KB](3)
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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
Establishing the structure-activity relationship of teixobactin
Matheson Eilidh , Jin Kang , Li Xuechen
2019, 30(8): 1468-1480  doi: 10.1016/j.cclet.2019.07.004
[Abstract](218) [FullText HTML] [PDF 3511KB](2)
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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.
Recent progress in transition metal catalyzed cross coupling of nitroarenes
Peng Lifen , Hu Zhifang , Tang Zilong , Jiao Yinchun , Xu Xinhua
2019, 30(8): 1481-1487  doi: 10.1016/j.cclet.2019.04.008
[Abstract](209) [FullText HTML] [PDF 1871KB](4)
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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.
Photo-promoted transition metal-free organic transformations in the absence of conventional photo-sensitizers
Jia Zhenhua , Yuan Yalin , Zong Xinlong , Wu Bingquan , Ma Jingyu
2019, 30(8): 1488-1494  doi: 10.1016/j.cclet.2019.04.073
[Abstract](204) [FullText HTML] [PDF 3633KB](2)
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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.
Recent advances of allenes in the first-row transition metals catalyzed C—H activation reactions
Han Xiang-Lei , Lin Peng-Peng , Li Qingjiang
2019, 30(8): 1495-1502  doi: 10.1016/j.cclet.2019.04.027
[Abstract](202) [FullText HTML] [PDF 3697KB](2)
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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.
Total syntheses of dehydrobotrydienal, dehydrobotrydienol and 10-oxodehydrodihydrobotrydial
Zhang Zichun , Zhao Dandan , He Yingdong , Yang Zhen , Gong Jianxian
2019, 30(8): 1503-1505  doi: 10.1016/j.cclet.2019.03.033
[Abstract](209) [FullText HTML] [PDF 1103KB](2)
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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.
A ketone-functionalized aromatic saddle as a potential building block for negatively curved carbon nanobelts
Cheung Kwan Yin , Miao Qian
2019, 30(8): 1506-1508  doi: 10.1016/j.cclet.2019.04.013
[Abstract](200) [FullText HTML] [PDF 2859KB](2)
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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.
Electrochemical synthesis of β-hydroxy-, β-alkoxy-, and β-carbonyloxy sulfones by vicinal difunctionalization of olefins
Zhang Zhefan , Yan Jiyao , Ma Dengke , Sun Jianwei
2019, 30(8): 1509-1511  doi: 10.1016/j.cclet.2019.04.023
[Abstract](185) [FullText HTML] [PDF 2446KB](2)
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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.
Diastereo- and enantioselective palladium-catalyzed dearomative [4+2] cycloaddition of 3-nitroindoles
Suo Jia-Jia , Du Juan , Jiang Yang-Jie , Chen Di , Ding Chang-Hua , Hou Xue-Long
2019, 30(8): 1512-1514  doi: 10.1016/j.cclet.2019.04.028
[Abstract](204) [FullText HTML] [PDF 1574KB](2)
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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.
Selective O-difluoromethylation of 1, 3-diones using S-(difluoromethyl) sulfonium salt
Liu Guo-Kai , Li Xin , Qin Wen-Bing , Lin Wei-Feng , Lin Li-Ting , Chen Jia-Yi , Liu Jian-Jian
2019, 30(8): 1515-1518  doi: 10.1016/j.cclet.2019.03.036
[Abstract](191) [FullText HTML] [PDF 2502KB](2)
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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.
Chiral iminophosphorane catalyzed asymmetric Henry reaction of α, β-alkynyl ketoesters
Zhang Yanxia , Wu Xin-Yan , Han Jianwei
2019, 30(8): 1519-1522  doi: 10.1016/j.cclet.2019.04.042
[Abstract](189) [FullText HTML] [PDF 1449KB](2)
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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).
Intramolecular (4+3) cycloadditions of nitrogen-tethered epoxy enosilanes for the synthesis of heteropolycycles
He Jiayun , Lam Shuk Mei , Ng Jerome P.L. , Wong Wing-Tak , Chiu Pauline
2019, 30(8): 1523-1526  doi: 10.1016/j.cclet.2019.04.051
[Abstract](195) [FullText HTML] [PDF 3073KB](2)
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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.
A facile synthesis of cajaninstilbene acid and its derivatives
Chen Qi , Lu Kuo , Zheng Chang , Xu Xiao-Fang , Lin Jing , Chen Wei-Min
2019, 30(8): 1527-1529  doi: 10.1016/j.cclet.2019.04.043
[Abstract](193) [FullText HTML] [PDF 2104KB](2)
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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.
How long a C–C bond can be? An example of extraordinary long C-C single bond in 1, 2-diarylamino-o-carboranes
Wu Yile , Zhang Jie , Xie Zuowei
2019, 30(8): 1530-1532  doi: 10.1016/j.cclet.2019.04.034
[Abstract](200) [FullText HTML] [PDF 1942KB](2)
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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.
Copper-mediated O-arylation of lactols with aryl boronic acids
Sui Jing-Jing , Xiong De-Cai , Ye Xin-Shan
2019, 30(8): 1533-1537  doi: 10.1016/j.cclet.2019.06.014
[Abstract](205) [FullText HTML] [PDF 2946KB](3)
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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.
Synthetic studies towards daphniyunnine B: Construction of AC bicyclic skeleton with two vicinal all carbon quaternary stereocenters
Sun Haiyu , Wu Guangmiao , Xie Xingang
2019, 30(8): 1538-1540  doi: 10.1016/j.cclet.2019.06.049
[Abstract](195) [FullText HTML] [PDF 1526KB](2)
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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.
A practical synthesis of β-carbolines by tetra-nbutylammonium bromide (TBAB)-mediated cycloaromatization reaction of aldehydes with tryptophan derivatives
Wang Zhen , Yu Zhenzhen , Yao Yao , Zhang Yakai , Xiao Xuefeng , Wang Bin
2019, 30(8): 1541-1544  doi: 10.1016/j.cclet.2019.07.001
[Abstract](191) [FullText HTML] [PDF 1926KB](2)
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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.
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