l-Proline-Catalyzed Three-Component Domino [3+2+1] Annulation for the Regio- and Diastereoselective Synthesis of Highly Substituted Thienothiopyrans Containing Three or Four Stereocenters

l-Proline-catalyzed three-component reactions of ethyl 2-[(2-oxo-2-arylethyl)sulfonyl]acetate or ethyl 2-[(2-ethoxy-2-oxoethyl)sulfonyl]acetate, aromatic aldehydes, and 5-aryltetrahydro-3-thiophenone furnished a variety of highly substituted thieno[3,2-c]thiopyran derivatives. This facile transformation presumably occurs via a one-pot domino sequence of enamine formation/aldol condensation/Michael addition/6-exo-trig cyclization/elimination and involves the creation in a single operation of three C−C bonds and the generation of three new stereocenters with complete diastereoselectivity in all cases and a fourth one in ca. 7:3 diastereomeric ratio when starting from a 5-substituted tetrahydro-3-thiophenone derivative.