共查询到20条相似文献,搜索用时 15 毫秒
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Chiral oxathianes were designed, synthesized, and successfully used for asymmetric sulfur ylide mediated epoxidation. A considerable emphasis has been placed upon the design of sulfides with suitable architecture in a small number of steps (three or four). The use of (4aR,6S,8aR)‐6‐isopropenyl‐8a‐methyloctahydro‐1,4‐benzoxathiane in asymmetric epoxidation resulted in good diastereo‐ and enantioselectivity in the formation of stilbene oxide, and (2S,6S)‐2‐allyl‐2,3,3,6‐tetramethyl‐1,4‐oxathiane produced even better results. Moderate to good diastereoselectivities with essentially complete enantioselectivities were observed in the formation of alkyl–aryl‐, vinyl–aryl‐, and propargyl–aryl‐substituted epoxides. The selectivities were rationalized and supported by density functional theory calculations. 相似文献
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Dr. Liang‐Qiu Lu Dr. Fang Li Jing An Ying Cheng Dr. Jia‐Rong Chen Prof. Dr. Wen‐Jing Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):4073-4079
A hydrogen‐bond‐mediated asymmetric [4+1] annulation/rearrangement cascade of stable sulfur ylides and nitroolefins was developed. This reaction provides a facile route to enantioenriched 4,5‐substituted oxazolidinones in moderate to excellent isolated yields (65–96 %) with excellent stereocontrol (up to more than 95:5 d.r. and 97:3 e.r.). This methodology was successfully applied to the concise synthesis of two bioactive molecules. The stereocontrolled modes and mechanism have been proposed to explain the origin of this stereochemistry. 相似文献
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Dr. Zhengxu S. Han Dr. Melissa A. Herbage Hari P. R. Mangunuru Yibo Xu Li Zhang Dr. Jonathan T. Reeves Dr. Joshua D. Sieber Dr. Zhibin Li Dr. Philomen DeCroos Dr. Yongda Zhang Dr. Guisheng Li Ning Li Dr. Shengli Ma Dr. Nelu Grinberg Dr. Xiaojun Wang Dr. Navneet Goyal Dr. Dhileep Krishnamurthy Dr. Bruce Lu Dr. Jinhua J. Song Dr. Guijun Wang Dr. Chris H. Senanayake 《Angewandte Chemie (International ed. in English)》2013,52(26):6713-6717
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Peng Jiao Dr. Masanori Kawasaki Dr. Hisashi Yamamoto Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(18):3333-3336
Chiral 1,2‐diols have been prepared from α‐aminoxylated aldehydes or cyclohexanone and Grignard reagents with L ‐proline or its tetrazole derivative as the catalyst. The presence of the ate complex of CeCl3?2 LiCl is essential for the high overall yields and good selectivities (see scheme; DMSO=dimethyl sulfoxide, THF=tetrahydrofuran, Tol=tolyl).
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《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(2):568-575
The reaction of ester‐stabilized sulfonium ylides with cyclopentenone to give (+)‐ 5 ((1S,5R,6S)‐ethyl 2‐oxobicyclo[3.1.0]hexane‐6‐carboxylate), an important precursor to the pharmacologically important compound (+)‐LY354740, has been studied using chiral sulfides operating in both catalytic (sulfide, Cu(acac)2, ethyl diazoacetate, 60 °C) and stoichiometric modes (sulfonium salt, base, room temperature). It was found that the reaction conditions employed had a major influence over both diastereo‐ and enantioselectivity. Under catalytic conditions, good enantioselectivity with low diastereoselectivity was observed, but under stoichiometric conditions low enantioselectivity with high diastereoselectivity was observed. When the stoichiometric reactions were conducted at high dilution, diastereoselectivity was reduced. This indicated that base‐mediated betaine equilibration was occurring (which is slow relative to ring closure at high dilution). Based on this model, conditions for achieving high enantioselectivity were established as follows: use of a preformed ylide, absence of base, hindered ester (to reduce ylide‐mediated betaine equilibration), and low concentration. Under these conditions high enantioselectivity (95 % ee) was achieved, albeit with low diastereocontrol. Our model for selectivity has been applied to other sulfonium ylide mediated cyclopropanation reactions and successfully accounts for the diastereoselectivity observed in all such reported reactions to date. 相似文献