Synthesis and Olfactory Evaluation of (+)- and (-)-gamma-Ionone

Abstract

The synthesis of enantiomerically pure (+)- and (−)-γ-ionone 3 is reported. The first step in the synthesis is the diastereoisomeric enrichment of 4-nitrobenzoate derivatives of racemic γ-ionol 12. The enantioselective lipase-mediated kinetic acetylation of γ-ionol 13b afforded the acetate 14 and the alcohol 15, which are suitable precursors of the desired products (−)- and (+)-3, respectively. The olfactory evaluation of the γ-ionone isomers shows a great difference between the two enantiomers both in fragrance response and in detection threshold. The selective reduction of (−)-3 and (+)-3 to the γ-dihydroionones (−)-(R)-16 and (+)-(S)-17, respectively, allowed us to assign unambiguously the absolute configuration of the γ-ionones.