Enantioselective synthesis of both enantiomers of gamma-ionone, gamma-damascone, karahana lactone and karahana ether

A straightforward enantioselective synthesis of both enantiomers of the title compounds is described starting from enantiopure methyl (2S,6R)- or (2R,6S)-cis-2-hydroxy-γ-cyclogeraniate. These versatile building blocks are obtained by biomimetic cyclization of methyl (6S)- or (6R)-(Z)-6,7-epoxy-7-methyl-3-(trimethylsilyl)methyl-2-octenoate, respectively. The chiral information was encoded by a highly regioselective Sharpless asymmetric dihydroxylation of the corresponding diene