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 di enophilic groups undergo intramolecular Diels-Alder (IMDA) reaction wi th high or complete selectivity for the cis-fused products. Incorporat ion of silyloxy groups within the carbon tether linking the diene and dienophile results in increased IMDA reactivity. The stereochemical ou tcomes of these processes are rationalised in terms of the preference for an exooriented phenylsulfonyl group, and a minimisation of non-bon ded interactions between the silyloxy and sulfone substituents.