Synthesis, olfactory evaluation and determination of the absolute configuration of the β- and γ-Iralia® isomers

The regioselective synthesis of the methyl-ionone isomers 6-9 is described. The enantiomers of the γ-isomers 8 and 9 are prepared by enzyme-mediated resolution of the corresponding 4-hydroxy derivatives followed by reductive elimination of the hydroxy group. The absolute configuration of the latter compound is determined by chemical correlation with the known α-isomers. Since all the isomers obtained are components of the artificial violet odourants sold under the trade name of Iralia®, their odour properties are evaluated by professional perfumers.