Used in combination with the Sharpless asymmetric epoxidation of allylicalcohols, this rearrangement represents a new approach to the synthesis of various opticallyactive β-hydroxy aldehydes, useful intermediates in natural product synthesis. The modified organoaluminum reagent, MABR is also applicable to the transformation of a variety of simple epoxides to carbonyl compounds with high efficiency
New General Method for Regio- and Stereoselective Allylic Substitution with Aryl and Alkenyl Coppers Derived from Grignard Reagents
作者:Yohei Kiyotsuka、Yuji Katayama、Hukum P. Acharya、Tomonori Hyodo、Yuichi Kobayashi
DOI:10.1021/jo802426g
日期:2009.3.6
Allylic substitution with sp2-carbon reagents (aryl and alkenyl anions) was realized by usingallylic picolinates and copper reagents derived from RMgBr and CuBr·Me2S to afford anti SN2′ products regio- and stereoselectively. Steric and electronic factors in the reagents and the size of the methylene substituents around the allylic moiety marginally affected the selectivity. The reaction system was
通过使用烯丙基吡啶甲酸酯和衍生自RMgBr和CuBr·Me 2 S的铜试剂实现Sp 2-碳试剂(芳基和烯基阴离子)的烯丙基取代,可以在区域和立体选择性地提供抗S N 2'产物。试剂中的立体和电子因素以及烯丙基部分周围的亚甲基取代基的大小在一定程度上影响了选择性。该反应系统也与烷基试剂相容。此外,该取代被应用于四元中心的构建和(-)-倍半茶烯酚的合成。吸电子的C的吡啶基的性质和螯合(═ ö)-C 5 H ^ 4 Ñ到MgBr 2 发现原位产生的碳负责替代的高效率。
Picolinoxy Group, a New Leaving Group for anti S<sub>N</sub>2′ Selective Allylic Substitution with Aryl Anions Based on Grignard Reagents
作者:Yohei Kiyotsuka、Hukum P. Acharya、Yuji Katayama、Tomonori Hyodo、Yuichi Kobayashi
DOI:10.1021/ol800300x
日期:2008.5.1
The picolinoxy group was found to be an extremely powerful leavinggroup for allylic substitution with aryl nucleophiles derived from ArMgBr and CuBr*Me2S. The substitution proceeds with anti SN2' pathway and with high chirality transfer. The electron-withdrawing effect of the pyridyl group and chelation to MgBr2 are likely the origin of success. Results suggesting these effects were obtained.
characteristic Lewis acid catalyst in the regio- and stereoselective rearrangement of epoxides to aldehydes. This Cr(TPP)OTf-catalyzed reaction is an operationally simple and especially convenient method for synthesizing optically active beta-siloxy aldehydes from 2,3-epoxy silyl ethers which are readily available in enantiomerically enriched forms by the Sharpless epoxidation of allylic alcohols followed