Synthesis and Absolute Stereochemistry of Chiral γ-Ionone and Dihydro-γ-ionone

Abstract

The optical resolution of (±)-α-cyclogeranic acid (4) with (—)-α-methylbenzylamine gave (—)-(S)-α-cyclogeranic acid (4). Epoxidation of (—)-(S)-methyl a-cyclogeranate (5), followed by reduction with lithium aluminum hydride, gave mainly (—)-(lR,2R)-2-hydroxy-2,6,6-trimethyl-1-cyclohexanemethanol (7b), which was oxidized with pyridinium chlorochromate to give (—)-hydroxyaldehyde 8. The reaction of aldehyde 8 with 2-oxopropylidenetriphenylphosphorane gave (—)-(l,S,2,R)-2‘,3,-dihydro-2’-hydroxy-α-ionone (9). The thermal decomposition of (l’S)-2’-acetoxy-2’3’-dihydro-α-ionone (10) gave (—)-(S)-α-ionone (2) and (+)-(S)-y-ionone (1). The partial hydrogenation of (+)-(5‘)-y-ionone (1) gave (+)-(S)-dihydro-y-ionone (3). © 1987, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.