Synthesis and odor of optically active 2-n-hexyl- and 2-n-heptylcyclopentanone and the corresponding δ-lactones

Enantiomeric 2-n-hexyl- and 2-n-heptylcyclopentanones (3) and (4) have been synthesized by asymmetric hydrogenation of 2-n-hexylidene and 2-n-heptylidenecyclopentanones (1) and (2) with Ru2Cl4[p-tolyl-binap]2NEt3 complexes. The differences in odor qualities between enantiomeric pairs of the ketones 3 and 4 have been found to be small, and the same odor threshold values have been observed between the enantiomeric pairs, although the corresponding δ-undeca- and δ-dodecalactones (6) and (7), synthesized by Baeyer–Villiger oxidation of the chiral ketones 3 and 4, showed a fairly large difference in the threshold values between the enantiomeric pairs.