Stereoselective Synthesis of 1,2,3‐Trisubstituted 1,3‐Dienes through Novel [3,3]‐Sigmatropic Rearrangements in α‐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 α‐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 α‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)