Asymmetric Michael reaction: novel efficient access to chiral β-ketophosphonates
摘要:
The asymmetric Michael reaction between chiral beta-enaminophosphonates derived from (S)-1-phenylethylamine and various electrophilic alkenes furnished beta,beta-disubstituted ketophosphonates in good yields and with excellent enantioselectivity. (c) 2007 Elsevier Ltd. All rights reserved.
In this work, the protecting-group-free total synthesis and stereochemical assignment of (−)-boscartin F have been reported. The key steps, including Sharpless asymmetric epoxidation, I2-mediated iodoetherification, aldol reaction, and ring-closing metathesis, allowed for rapid and highly stereoselective access to boscartin F. In addition, single-crystal X-ray crystallographic analysis of the semicarbazone
Decarboxylative Grob-Type Fragmentations in the Synthesis of Trisubstituted<i>Z</i> Olefins: Application to Peloruside A, Discodermolide, and Epothilone D
作者:Kathrin Prantz、Johann Mulzer
DOI:10.1002/anie.200901740
日期:2009.6.22
elimination: A new method for the synthesis of methyl‐branched trisubstituted Z olefins, a structural motif in many polyketides with anticancer activity, relies on an −OH‐induced decarboxylative Grob‐type fragmentation (see scheme; Ms=mesyl). The starting materials are β‐mesyloxy lactones with a quaternary α center, which are prepared by aldol reactions in a diastereo‐ and enantioselective manner.
判别消除:为甲基支化的三取代的合成的新方法Ž 烯烃,具有抗癌活性的许多聚酮化合物的结构基序,依赖于- OH诱导脱羧格罗型片段化(参见方案; MS =甲磺酰基)。起始原料是具有季α中心的β-甲氧基内酯,它们是通过非对映和对映选择性的醛醇缩合反应制备的。
Synthesis of Multisubstituted 1,2,3-Triazoles: Regioselective Formation and Reaction Mechanism
synthetically useful approach to functionalized triazoles is described via the reaction of β-carbonyl phosphonates and azides. 1,4- and 1,5-disubstituted and 1,4,5-trisubstituted triazoles can be regio- and chemoselectively accessed under mild conditions in good to excellent yields (31 examples, up to 99%). A mechanism is proposed that rationalizes the avoidance of the 4-phosphonate byproducts, which