Chemistry of tetra-alkoxyethenes. Part VII. Thermal [2 + 2] cyclo-additions with 1-cyanobutadienes

Abstract

Acyclic 1-cyanobutadienes (2) having a second electron-withdrawing substituent at C-1 behave towards tetra-alkoxyethenes (1) like equally substituted simple olefins. The normal product is a [2 + 2], not a [4 + 2] cyclo-addition product. The correspondence in reactivity of these electron-poor olefins and butadienes towards the nucleophilic tetra-alkoxyethenes is further exemplified by the similarity of substituent effects on the cycloadditions. A possible explanation is given.