Synthesis of (+)- and (-)-cis-α-Irones

Abstract

A stereocontrolled total synthesis of natural (+)-cis-α-irone (1) is described. The key intermediate (±)-hemiacetal 15 was prepared from the diene 10 in six steps. The crucial optical resolution of (±)-15 was achieved by initial stereoselective conversion into the corresponding l-menthyl acetals 16 and 17 followed by separation and hydrolysis. One of the optically pure enantiomers of 15 was transformed to (-)-18 and then to (+)-1 in seven steps. The synthetic (+)-1 was found to be identical with the natural (+)-cia-α-irone. The isomeric (-)-cis-α-irone was also synthesized from the other enantiomer of 15, via (+)-18.