Cyclopropacycloheptathiophenones and thiols: unexpected rearrangement with dithiols leading to benzo- and cyclo-octa-thiophenes. Spectroscopic and mechanistic studies

Abstract

Cyclopropa[3,4]cyclohepta [1,2-c]thiophen-5-one reacts in an acidic medium with thiols to give addition or rearrangement compounds: [1,4] addition occurs with ethanethiol, but with 2-mercaptoethanol isomerization of the cyclopropyl ring to a vinyl group occurs, and the thioacetal was not obtained. The most surprising results are observed with ethane-1,2-dithiol and propane-1,3-dithiol, where a benzo[b]thiophene is isolated. An X-ray analysis of the latter compound and appropriate deuterium labelling experiments led us to propose a possible mechanism for this unexpected reaction pathway.