Stereoselective construction of cycloheptene-fused indoline frameworks through photosensitised formal [5+2] cycloaddition

Abstract

Irradiation of 1-acylindole derivatives that possess a vinylcyclopropane moiety at the end of the acyl side chain by a high-pressure mercury lamp through Pyrex glass under sensitization of an aromatic ketone gave the corresponding cyclised products stereoselectively in high yields. The distribution of the products was highly dependent on the substituents on the cyclopropane ring. In the case of a simple cyclopropane, the product was a mixture of ring-expanded cycloheptene-fused indoline and all-cis-fused cyclopropylcyclobutane-fused indoline through [2 + 2] cycloaddition, while cycloheptene-fused indolines were predominantly produced via formal [5 + 2] cyclisation in the case of substituted cyclopropanes. In particular, the product selectivity was substantially high in the case of silylcyclopropane.