Dimerisation of 3-aryl-2-cyanothioacrylamides. A [2s+ 4s] cyclo-addition to give substituted 3,4-dihydro-2H-thiopyrans

Abstract

A thermal dimerisation of the Diels–Alder type is reported for certain 3-aryl-2-cyanothioacrylamides giving rise to novel derivatives of 3,4-dihydro-2H-thiopyran. The regioselectivity and stereoselectivity of this thermal heterodiene cycloaddition reaction are rationalised in terms of frontier orbital interactions. N.m.r. and i.r. data are reported for 21 thioacrylamides in monomeric and/or dimeric form.