Enantioselective synthesis and olfactory evaluation of 13-alkyl-substituted alpha-ionones.
To study the influence of the steric bulk of the substituents at C(5) on the olfactory characteristics of alpha-ionone, the (S)-antipodes of compounds 8-10 were synthesized starting from (S)-alpha-cyclogeraniol (14a). The latter was available in useful preparative yield with 95% ee by enantioselective lipase-PS-mediated acetylation of the racemic mixture. Key step in the conversion of 14a to 8-10 was an S(N)2'-type reaction of an organocuprate on the allylic phosphate 20, which appears to be a general method for the introduction of an alkyl substituent at the cyclohexene C=C bond of ionones. Olfactory evaluation showed that, compared to the parent (S)-alpha-ionone (1), the odor strength and fragrance facets of the three analogues 8-10 are significantly influenced by the bulkiness of the substituent at C(13), giving further evidence that hydrophobic interactions of this group play a significant role in the chemoreception of ionones. In particular, the odor of the ethyl derivative 8 was found to be significantly stronger than that of the parent (S)-alpha-ionone (1).
Luparia
Marco
M
Dipartimento di Chimica Organica, Università di Pavia, Via Taramelli 10, I-27100 Pavia.
Boschetti
Paolo
P
Piccinini
Francesca
F
Porta
Alessio
A
Zanoni
Giuseppe
G
Vidari
Giovanni
G
D015394:Molecular Structure; D045792:Norisoprenoids / Q000138:chemical synthesis* / Q000737:chemistry; D009812:Odorants / Q000032:analysis*; D010476:Perfume / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D045792:Norisoprenoids; D010476:Perfume; C011879:alpha-ionone