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  • Enantioselective synthesis and olfactory evaluation of 13-alkyl-substituted alpha-ionones.

Enantioselective synthesis and olfactory evaluation of 13-alkyl-substituted alpha-ionones.

Chemistry & biodiversity (2008-07-12)
Marco Luparia, Paolo Boschetti, Francesca Piccinini, Alessio Porta, Giuseppe Zanoni, Giovanni Vidari
ABSTRACT

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).

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
α-Ionone, technical grade, 90%
Sigma-Aldrich
α-Ionone, ≥90%, stabilized