| Abstract: | Enantioselective total syntheses of the four stereoisomers of the fragrance Magnolione® ( 1 ) are described. Key step is a Pd‐catalyzed asymmetric allylic alkylation displaying enantiomer excess of ≥ 99% (Scheme 2). The resultant methyl α‐acetyl‐2‐pentylcyclopent‐2‐ene‐1‐acetate) was subjected to demethoxycarbonylation, carbonyl protection by acetalization, and epoxidation (Schemes 2 and 3). Subsequent Lewis acid catalyzed epoxide/ ketone rearrangement followed by deprotection gave cis/trans mixtures of Magnolione® in 28% overall yield (Scheme 3). The cis/trans isomers were separated by prep. HPLC, and fragrance properties as well as odor threshold values were determined (Table 2). |
