Stereoselective synthesis of 1,2,3-trisubstituted 1,3-dienes through novel [3,3]-sigmatropic rearrangements in alpha-allenic methanesulfonates: Application to the preparation of fused tricyclic systems by tandem rearrangement/Diels-Alder reaction

An unprecedented stereoselective and general synthesis of 1,2,3-trisubstituted 1,3-dienes' from alpha-allenols just by treatment with a methanesulfonyl chloride/tertiary amine system has been developed. This transformation might be tentatively explained in terms of a migration of the methanesulfonyl group in the initially formed alpha-allenic methanesulfonate to give the corresponding mesyloxy-diene through a [3,3]-sigmatropic rearrangement. This reactivity pattern was incorporated into a domino process, allowing the development of a novel one-pot synthetic strategy for the preparation of fused tricycles from monocyclic allenols, masked functionalized dienes, when subjected to a domino allenol transposition/intramolecular Diels-Alder reaction process. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.