Homogeneous asymmetric catalysis in fragrance chemistry

Opposite enantiomers of a chiral fragrance may exhibit different olfactory activities making a synthesis in high enantiomeric purity commercially and scientifically interesting. Accordingly, the asymmetric synthesis of four chiral odorants, Fixolide (R), Phenoxanol (R), Citralis (R), and Citratis Nitrile (R), has been investigated with the aim to develop practically feasible processes. In the devised synthetic schemes, the key step that leads to the formation of the stereogenic center is the homogeneous asymmetric hydrogenation of a prochiral olefin. By an appropriate choice of the catalyst and the reaction conditions, Phenoxanol (R), Citralis (R), and Citralis Nitrile (R) were obtained in high enantiomeric purity, and odor profiles of the single enantiomers were determined.