Lipase-mediated synthesis of the enantiomeric forms of 4,5-epoxy-4,5-dihydro-alpha-ionone and 5,6-epoxy-5,6-dihydro-beta-ionone. A new direct access to enantiopure (R)- and (S)-alpha-ionone.

Stereoselective lipase-mediated esterifications of epoxy-alpha-ionol 5 and epoxy-beta-ionol 9 afforded suitable precursors of the enantiomers of the corresponding oxidised derivatives epoxy-alpha-ionone 3 and epoxy-beta-ionone 4. An interesting development of this work is the easy conversion of enantiopure 3a and 3b into highly valuable enantiopure (S)- and (R)-ionone (1a and 1b) via a mild deoxygenation reaction.