Synthesis, olfactory evaluation and determination of the absolute configuration of the beta- and gamma-Iralia (R) isomers

The regioselective synthesis of the methyl-ionone isomers 6-9 is described. The enantiomers of the 7-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 alpha-isomers. Since all the isomers obtained are components of the artificial violet odourants sold under the trade name of Iralia (R), their odour properties are evaluated by professional perfumers.