Synthesis of Substituted 4H-Thiochromen-4-imines via Copper-Catalyzed Cyclization Cascades of o-Bromobenzothioamides with Terminal Alkynes

A series of (E)-N-aryl-4H-thiochromen-4-imines has been conveniently obtained through a cascade reaction between o-bromobenzothioamides and terminal alkynes. This novel approach probably involved an initial generation of benzothietane-2-imine intermidates via an intramolecular Ullmann reaction under CuI/L-proline cocatalysis and alkaline conditions followed by imine alkynylation, ring opening, and cyclization sequences to provide the unexpected 4H-thiochromen-4-imines rather than isothiochromans.