Fully Substituted Thiophene Synthesis via (3 + 2) with Thiadiazoles

A method to access highly substituted dihydrothiophenes and the corresponding thiophenes is reported. This strategy complements traditional stepwise synthesis by coupling readily accessible bicyclic 1,2,3 thiadiazoles with alkenes in a modular, Rh-catalyzed formal (3 + 2) cycloaddition. Application of this method to an array of novel thiadiazoles generates densely functionalized dihydrothiophenes that can be subsequently oxidized to the corresponding thiophene products.