Enamino ketones as precursors of functionalised 2H-thiopyrans and thiopyrano[2,3-c]- and [3,2-b]-benzothiopyrans

Abstract

Oxo enamino ketones obtained by treating active methylene compounds with N,N-dimethylformamide dimethyl acetal yield novel 2H-thiopyrans in a regioselective one pot thionation–[4 + 2]-cycloaddition sequence. Application of similar methodology to thiochroman-3-ones affords novel thiopyrano[2,3-c][1]benzothiopyrans and the [3,2-b] isomers.