Synthetic applications of enantioselective protonation and case study for (S)-alpha-damascone.
Among the fragrance compounds synthesized by enantioselective protonation, (S)-alpha-damascone, (R)-muscone, and (S,S)-Vulcanolide are the most prominent ones. (S)-alpha-damascone has been prepared by four different procedures: from the magnesium enolate, from the lithium enolate, from the enol, and from the corresponding thiol ester. We now present a new, industrially viable protocol for the addition of allyl magnesium chloride to the 'cyclogeranoketene' by a Barbier reaction, followed by protonation of the ensuing magnesium enolate by an aggregate formed from (-)-N-isopropylephedrine, lithium isopropylate, and acetic acid, furnishing (S)-alpha-damascone in 91% yield and with 71% ee.
Fehr
Charles
C
Firmenich SA, Corporate R&D Division, P. O. Box 239, CH-1211 Geneva 8. charles.fehr@firmenich.com
Randall
Harvey
H
D015394:Molecular Structure; D045792:Norisoprenoids / Q000138:chemical synthesis* / Q000737:chemistry; D009812:Odorants / Q000032:analysis; D010476:Perfume / Q000138:chemical synthesis* / Q000737:chemistry; D011522:Protons; D013237:Stereoisomerism; D013696:Temperature
D045792:Norisoprenoids; D010476:Perfume; D011522:Protons; C496116:alpha-damascone