Regioselective Synthesis of Dihydrothiophene and Thiopyran Frameworks via Catalyst-Controlled Intramolecular Cγ/Cδ–S Fusion of α-Allyl-β′-oxodithioesters

Abstract

A highly efficient and atom-economic dual reaction manifold has been developed to synthesize 4H-thiopyran and 4,5-dihydrothiophene frameworks via regioselective intramolecular C–S fusion of α-allyl-β′-oxodithioesters. The ring size of the sulfur-heterocycles has been efficiently tuned by the use of two different catalytic systems. Palladium activates the Cδ–H of the allyl termini and facilitates the intramolecular Cδ–S coupling to furnish six-membered thiopyran skeletons exclusively. Conversely, the allylic double bond of the same substrate has been activated by BF3·Et2O to promote the Cγ–S cyclization leading to the formation of a five-membered dihydrothiophene nucleus.