Mechanistic insights into the thermal transformations of heterocyclic o-distyrylbenzenes: an experimental and computational study

Abstract

The thermal transformations of various –CH₃/–H thienyl and furyl derivatives of o-divinylbenzenes in acidic media are presented. Experimental and theoretical studies were carried out to elucidate the mechanism. The formation of all furyl electrocyclization products 5–7 could be explained via mechanisms that begin with the [4+2] cycloaddition process of the starting compound. In the last step, either the release of a proton or a furyl group takes place, depending on the product formed. The mechanism of formation of indane/indene furyl 8 and 9 and thienyl thermal products III–VI starts with protonation of the double bond of the starting compound and 1,5-ring closure to give a carbocation intermediate, followed by a protonation/deprotonation process, respectively. All computational data, derived from quantum chemical DFT calculations, are in agreement with experimental results.