Further rearrangements of cyclopropyl epoxides. Formation of cyclobutanes and cyclobutenes

Abstract

Cyclopropyl epoxides having aryl substituents in the 1 -position of the cyclopropane ring underwent acid-catalysed rearrangement to Iand 2-arylcyclobutenes ; in methanol they formed stereoisomeric 1 -aryl-I -methoxycyclobutanes. A cyclopropyl epoxide substituted in the 2-position of the cyclopropane ring by geminal methyl groups rearranged to a hexa-2.5-dien-I -01 rather than a 3.6-dihydro-2H-pyran. Except in the formation of stereoisomeric pent-2-en-I -01s. cyclopropyl epoxides unsubstituted in the alicyclic ring underwent typical epoxide reactions. THE rearrangement of oxirans having a contiguous cyclopropane ring has been the subject of recent studies. Prinzbach and Fischer proposed that the rearrangement of an oxabicyclobutane intermediate (11) best accounts for the products obtained in the reaction of a cyclopropene (I) with peracetic acid. This proposal is supported by later work.2 The oxaspiropentane system has been the subject of a detailed study.3 Its characteristic rearrangement is to form a cyclobutanone, as exemplified4 by the parent compound (111). The