Construction of Fused Medium‐Ring Carbocycles by Catalytic Generation and Rearrangement of Oxonium Ylides

Fused carbocyclic systems containing seven- and eight-membered rings can be constructed from allylic ethers in a stereoselective manner by tandem carbenoid generation, ylide formation and [2,3] rearrangement. Exceptionally high yields are obtained in cases where the substrate possesses favourable relative stereochemistry. The dienes resulting from [2,3] rearrangement of gem-divinyl ylides undergo Diels–Alder cycloaddition with reactive dienophiles at room temperature. Ylide formation, rearrangement and cycloaddition can be performed in a one-pot process to generate complex tetracyclic systems in a highly stereoselective manner. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)