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Enantioselective Synthesis and Olfactory Evaluation of 13‐Alkyl‐Substituted α ‐Ionones
Author(s) -
Luparia Marco,
Boschetti Paolo,
Piccinini Francesca,
Porta Alessio,
Zai Giuseppe,
Vidari Giovanni
Publication year - 2008
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200890084
Subject(s) - chemistry , substituent , enantioselective synthesis , odor , steric effects , allylic rearrangement , stereochemistry , alkyl , organic chemistry , catalysis
To study the influence of the steric bulk of the substituents at C(5) on the olfactory characteristics of α ‐ionone, the ( S )‐antipodes of compounds 8 – 10 were synthesized starting from ( S )‐ α ‐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 CC bond of ionones. Olfactory evaluation showed that, compared to the parent ( S )‐ α ‐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 )‐ α ‐ionone ( 1 ).