Thermal fragmentation of 2-azidobenzo[b]thiophene in the presence of alkenes: a new synthetic route to 1-(2-benzo[b]thienyl)aziridines and/or thiochroman-4-carbonitriles

Abstract

Mild thermal fragmentation of 2-azidobenzo[b]thiophene in the presence of olefins results in the formation of 1-(2-benzo[b]thienyl)aziridines and/or 4-cyanothiochromans in fairly good yields. The formation of aziridines, at the expense of thiochromans, is favoured by electron-poor olefins and by a decrease in the reaction temperature. Evidence is presented in favour of a singlet nitrene intermediate which adds to the olefin double bonds or undergoes a ring-opening reaction to give an ortho-quinoidal enethione which is trapped by the alkene present. These findings provide the first example of ready ring-opening by a 2-nitreno substituted thiophene.