Facial selectivity in the reactions of 1,3-dipoles with cis- and trans-3,4-dimethyl-1-methoxycarbonyl cyclobutenes
作者:Enrico Cinquini、Mauro Freccero、Remo Gandolfi、Mirko Sarzi Amade'、Augusto Rastelli
DOI:10.1016/s0040-4020(97)00539-5
日期:1997.7
diastereoselectivity is observed only in the case of the reaction of 3b with 3,4-dihydroisoquinoline-N-oxide (anti/syn = 94:6) while face selectivity decreases in the reaction of 3b with diazomethane (anti/syn = 72:28) and there is a reversal of face selectivity in the reactions of 3b with nitrile oxides (anti/syn ≈ 42:58). In the latter reaction the dominant syn diastereoisomer is formed via the sterically
1,3-偶极[重氮甲烷(5),3,4-二氢异喹啉-N-氧化物(6)和腈类氧化物(7)]与反式3,4-二甲基-1-甲氧基羰基环丁烯的区域选择性反应的面部选择性(4)通过与主导形成反非对映体的空间位阻因素的控制(抗/顺式:82:18为5,54:46为6和用于≈74:26 7)通过在空间上不那么拥挤过渡状态。传递至顺式3,4-二甲基-1-甲氧基羰基环丁烯(3b)时,仅在3b反应的情况下才观察到非对映选择性的预期增加用3,4-二氢异喹啉-N-氧化物(anti / syn = 94:6),而3b与重氮甲烷(anti / syn = 72:28)的反应中面选择性降低,并且反应中的面选择性逆转的图3b与氧化腈(抗/顺≈42:58)。在后一反应中,主要的顺式非对映异构体是通过空间上更拥挤的TS形成的。在3b与1,3-偶极子的反应中明显存在顺取向电子效应(尚未明确鉴定),在3b与腈氧化物的反应中,它具有足够强的强度来克服相关的抗取向空间效应。