endo-selective intramolecular Pauson-Khand reactions of gamma-oxygenated-alpha,beta-unsaturated phenylsulfones

A wide variety of 1,6-enynes and 1,7-enynes incorporating gamma -oxygenated -alpha,beta -unsaturated phenylsulfone moieties have readily been prepared by piperidine-promoted condensation of the corresponding alkynyl aldehyde w ith phenylsulfonyl-(p-tolylsulfinyl)methane and further protection of the h ydroxyl group. Despite the enduring claim concerning the unsuitability of e lectronically deficient olefins in Pauson - Khand reactions, we report that these 1-sulfonylated enynes are excellent substrates in intramolecular Pau son - Khand reactions under both thermal and amine N-oxide-promoted conditi ons. Moreover, in contrast with the usual exo-selective Pauson - Khand cycl ization of allylic substituted enynes. the reactions of these 1-sulfonylate d-3-oxygenated enynes occur with a moderate or high endo selectivity. The e valuation of the chemical and stereochemical scope of the process in compar ison with the Pauson - Khand cyclization of non-sulfonylated enynes, its ap plication to the stereoselective preparation of optically pure C6-substitut ed bicyclo[3.3.0]oct-1-en-3-ones. and the interpretation of the stereochemi cal outcome are also the discussed.