A Novel Cyclopentene Annulation Method Based on Conjugate Addition Reactions of α‐Cyano Carbanion Species

A new cyclopentene annulation method based on a conjugate addition reaction with 4-methoxybut-3-enenitrile was developed. Treatment of a cyclic enone with the potassium carbanion of the nitrile followed by acetic anhydride afforded an enol acetate, which underwent an HCl-mediated intramolecular cyclization reaction to yield a bicyclo[n.3.0]alkenone derivative in good yield. A lipase-mediated optical resolution of the annulation product provided a new chiral building block for steroids and other natural compounds.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)