Catalytic Asymmetric Synthesis of Quaternary Carbon Centers. Exploratory Studies of Intramolecular Heck Reactions of (<i>Z</i>)-α,β-Unsaturated Anilides and Mechanistic Investigations of Asymmetric Heck Reactions Proceeding via Neutral Intermediates
作者:Atsuyuki Ashimori、Benoit Bachand、Michael A. Calter、Steven P. Govek、Larry E. Overman、Daniel J. Poon
DOI:10.1021/ja980787h
日期:1998.7.1
Intramolecular Heckreactions of seven (Z)-α,β-unsaturated 2-iodoanilides catalyzed by Pd−BINAP were surveyed using two reaction conditions: (1) silver-promoted cyclizations in the presence of 2 equiv of Ag3PO4 and (2) base-promoted cyclizations in the presence of 4 equiv of 1,2,2,6,6-pentamethylpiperidine (PMP). A comparison of these results with the outcome of the corresponding intramolecular Heck reactions
使用两种反应条件调查了由 Pd-BINAP 催化的七种 (Z)-α,β-不饱和 2-碘代苯胺的分子内 Heck 反应:(1) 在 2 当量 Ag3PO4 和 (2) 碱-在 4 当量的 1,2,2,6,6-五甲基哌啶 (PMP) 存在下促进环化。将这些结果与 E 立体异构体的相应分子内 Heck 反应的结果进行比较,得出以下结论:(1) (E)- 和 (Z)-α,β-不饱和 2-碘代苯胺给出了 Heck 的相反对映异构体 为 HI 受体时的产物(阳离子途径);当 HI 受体是 PMP(中性途径)时,产物的绝对构型与烯烃几何形状无关。(2) 当 2-取代基是 Me 或伯烷基时,立体诱导在 PMP 促进的 Z 底物插入中是最佳的,其中 ee 高达 97%。(3) 当 2-取代基很大时,立体诱导在 E 底物存在下进行插入时是最佳的...
Asymmetric synthesis of carbohydrates: Synthesis of 2-deoxy-D- and 2-deoxy-L-xylofuranosides from a simple achiral precursor
作者:Michael E. Jung、John M. Gardiner
DOI:10.1016/s0040-4039(00)73487-3
日期:1994.9
3, readily prepared in two steps from propargyl bromide, 1, is converted to methyl 2-deoxy-D-xylofuranoside, 13, and to the unnatural L-enantiomer, 12, in 5 steps and 50% overall yield, utilizing asymmetric dihydroxylation (AD) of alkene 7 for introduction of chirality. A similar strategy from the isomeric Z-allylic alcohol, 4, afforded the 2-deoxy-L-ribofuranoside, but in modest enantiomeric excess
An efficient approach to (-)-mitralactonine using Pictet-Spengler cyclisation with a highly functionalised masked aldehyde is described. Sharpless asymmetric dihydroxylation (SAD) is utilised to introduce chirality in the key substrate.