Thionation reactions of 2-pyrrole carboxylates

Abstract

Reaction of 2-pyrrole carboxylates with Lawesson's reagent at elevated temperatures results in the corresponding thionoesters, concurrent with the production of a new class of pyrrole annulated with the (1,3,2)-thiazaphospholidine unit. X-ray crystallography was used to identify the pyrrolic thiazaphospholidine, which was found to have unique structural features compared to literature analogues. Addition of BF₃·OEt₂ to the thionation procedure was found to produce the corresponding F-BODIPY, constituting a four-step reaction in one-pot. The scope and limitations of these reactions involving the promiscuous Lawesson's reagent are discussed herein.