[3,2] Sigmatropic rearrangements of some allylic oxosulphonium ylides. A route to trienes and azatrienes, and their cyclic isomers

Abstract

The imidoyl-substituted oxosulphonium ylides (2) reacted with dimethyl acetylenedicarboxylate and with di-benzoylacetylene by conjugate addition. The resulting allylic oxosulphonium ylides underwent [3,2] sigmatropic rearrangement at room temperature or below, to give the sulphoxides (3). These sulphoxides readily lost methane-sulphinic acid when heated at 80 °C and gave the dihydropyridines (4). These reactions are presumed to go by way of intermediate azatrienes (6). The stabilised oxosulphonium ylides (7) reacted with dimethyl acetylenedicarboxylate by a similar sequence which gave the isolable trienones (9). These trienones underwent electrocyclic ring-closure when heated in xylene.