N‑Heterocyclic Carbene-Catalyzed Atom-Economical and Enantioselective Construction of the C–S Bond: Asymmetric Synthesis of Functionalized Thiochromans

An N-heterocyclic carbene-catalyzed cleavage and recombination of the C–S bond was developed. This is an efficient example of NHC reacting with an unsaturated thioester to generate an α,β-unsaturated acyl azolium with high atom economy. This protocol affords an alternative route for the construction of highly functionalized thiochroman derivatives with three consecutive stereogenic centers with good to high yields, as well as excellent diastereoselectivity and enantioselectivity.