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.