Asymmetric [2+2+1] cyclopentannulation of olefins. Ring expansion of 2-N-methyl-N-tosyl-cyclobutanone
作者:Florence Mahuteau-Betzer、Léon Ghosez
DOI:10.1016/s0040-4020(02)00694-4
日期:2002.8
factors which have been analyzed. Treatment of these oxiranes with a stoichiometric amount of lithium iodide in refluxing tetrahydrofuran gave excellent yields of monocyclic or fused cyclopentenones 4 resulting from a β-elimination of N-methyl-N-tosylamide from a primarily formed cyclopentanone. The ring-expansion was totally selective but for oxiranes attached to a bicyclo[4.2.0]octanone system. In all
先前已经以高收率和高对映体过量由烯烃和手性酮亚胺盐制备的α- N-甲基-N-甲苯磺酰基环丁酮2已经通过与二甲基s甲基化反应而转化为相应的环氧乙烷3。发现该反应的立体化学取决于已分析的几个因素。在回流的四氢呋喃中用化学计量的碘化锂处理这些环氧乙烷,可得到极佳的单环或稠合环戊烯酮4的收率,这是由于β-消除了N-甲基-N最初形成的环戊酮生成的对甲苯磺酰胺。环的扩展是完全选择性的,但是对于连接在双环[4.2.0]辛烷酮系统上的环氧乙烷而言。在所有情况下,在整个序列中都保留了起始环丁酮的对映体纯度,因此代表了一种有用的[2 + 2 + 1]策略用于烯烃的环戊烯环化。