γ-oxygenated-α,β-unsaturated sulfones in radical cyclizations and cascade processes

A wide variety of radical precursors having the structure of gamma-oxygenated-alpha,beta-unsaturated sulfone (substrates 1-4) have been prepared. Both 5-hexenyl and 6-heptenyl radicals, generated by reaction of substrates 1-4 with Bu3SnH/AIBN, underwent an efficient cyclization via intramolecular addition to the vinyl sulfone moiety. By introduction of a double bond joined to the oxygen at gamma-position, a cascade process based on two sequential radical cyclizations took place, affording highly substituted 2-oxa[3.3.0] or 9-oxa[4.3.0] bicyclic compounds. (C) 1998 Elsevier Science Ltd. All rights reserved.