Synthesis and olfactory evaluation of (+)- and (-)-gamma-ionone

The synthesis of enantiometically pure (+)- and (-)-gamma -ionone 3 is repo rted. The first step in the synthesis is the diastereoisomeric enrichment o f 4-nitrobenzoate derivatives or racemic gamma -ionol 12. The enantioselect ive lipase-mediated kinetic acetylation of gamma -ionol 13b afforded the ac etate 14 and the alcohol 15, which are suitable precursors of the desired p roducts (-)- and (+)-3, respectively. The olfactory evaluation of the gamma -ionone isomers shows a great difference between the two enantiomers both in fragrance response and in detection threshold. The selective reduction o f (-)-3 and (+)-3 to the gamma -dihydroionones (-)-(R)-16 and (+)-(S)-17, r espectively, allowed us to assign unambiguously the absolute configuration of the gamma -ionones.