The chemistry of Zerumbone IV: Asymmetric synthesis of Zerumbol

The achiral sesquiterpene zerumbone (1), readily available from a wild ginger, has unique functionality and reactivity which make it a potential starting material for conversion to useful compounds such as paclitaxel, provided that it can easily be transformed to chiral derivatives. Optically active zerumbol 2 and its acetate 3 were synthesized by lipase-catalyzed stereoselective transesterification of racemic 2. In the best conditions found, a lipase from Pseudomonas fluorescens (Amano AK) and isopropenyl acetate in THF at 30 °C afforded (R)-2 and (S)-3 with an E value of 56. The absolute configuration of (R)-2 was determined by Sharpless epoxidation with l-diethyltartrate (l-DET) to a bisepoxide of known configuration.