Syntheses of Enantiomerically Pure Cyclopent‐2‐ene‐1‐carboxylic Acid and (Cyclopent‐2‐enyl)acetic Acid by Enantioselective Palladium‐Catalyzed Allylic Alkylations − Synthesis of Enantiomerically Pure (−)‐Chaulmoogric Acid

Asymmetric Pd‐catalyzed allylic alkylations of dimethyl malonate and diethyl 2‐acetoxymalonate with 3‐chlorocyclopentene, using phosphanyloxazolines 1 and ent‐1 as chiral ligands, gave products (−)‐2 and (+)‐3b with 95 and 99.5% ee, respectively. Oxidative degradation of (+)‐3b furnished (+)‐(R)‐cyclopent‐2‐ene‐1‐carboxylic acid [(+)‐4] with > 99% ee. Alkylation product (−)‐2 was transformed into enantiomerically pure (−)‐(R)‐(cyclopent‐2‐enyl)acetic acid [(−)‐5] by three simple steps. Availability of (−)‐5 enabled the first synthesis of enantiomerically pure (−)‐chaulmoogric acid [(−)‐9] in three steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)