INTRAMOLECULAR DIELS-ALDER REACTIONS OF INTERNALLY-SUBSTITUTED TRIENYLSULFONES - SYNTHESIS OF BICYCLO[4.3.0] AND BICYCLO[4,4.0] SYSTEMS POSSESSING A BRIDGEHEAD SULFONYL GROUP

A series of trienes possessing internally-activated vinylic sulfone dienophilic groups undergo intramolecular Diels-Alder (IMDA) reaction with high or complete selectivity for the cis-fused products. Incorporation of silyloxy groups within the carbon tether linking the diene and dienophile results in increased IMDA reactivity. The stereochemical outcomes of these processes are rationalised in terms of the preference for an exooriented phenylsulfonyl group, and a minimisation of non-bonded interactions between the silyloxy and sulfone substituents.