Asymmetric Catalytic Synthesis of Thiochromenes via an Acyl Transfer-Initiated Cascade

A novel, reagent-free catalytic transformation of α,β-unsaturated thioesters into 2-substituted thiochromenes has been developed, with carbon dioxide as the only byproduct. Amidine-based catalysts, particularly homobenzotetramisole and its analogues, achieve high enantioselectivities and yields in this process.