Stereoselective cyclopropanation of enones with ethyl dimethylsulfonium acetate bromide in the presence of DBU
作者:Iván Collado、Carmen Domínguez、Jesús Ezquerra、Concepción Pedregal、James A Monn
DOI:10.1016/s0040-4039(97)00265-7
日期:1997.3
The cyclopropanation reaction of α, β-unsaturated ketones 1a-c with ethyl (dimethyl sulfuranylidene) acetate (EDSA), generated in situ from the corresponding sulfonium bromide salt and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) in toluene, leads exclusively to the exo adduct 2a-c (d.e.=100%). Acyclic enones 1d-g, give mainly the “trans” cyclopropanes 4d-g with a high degree of stereocontrol (d.e.380%)
α的环丙烷化反应,β不饱和酮1A-1C用乙酸乙酯(二甲基sulfuranylidene)乙酸酯(EDSA),产生在原位由相应的锍溴化物盐和1,8-二氮杂双环[5,4,0]十一碳-7-甲苯中的烯烃(DBU)仅导致外加合物2a-c(de = 100%)。无环烯酮1d-g主要产生具有高度立体控制度的“反式”环丙烷4d-g(3 3 80%)。将溶剂改变为CHCl 3分别得到“反式”和“顺式”环丙烷4d-g和5d-g的2:1混合物。“顺式”异构体5d-g在基本条件下可以被异构化为替代的“反式”异构体6d-g。