Synthetic Applications of Enantioselective Protonation and Case Study for (S)-α-Damascone

✍ Scribed by Charles Fehr; Harvey Randall

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 298 KB
• Volume: 5
• Category: Article
• ISSN: 1612-1872
• DOI: 10.1002/cbdv.200890106

✦ Synopsis

Abstract

Among the fragrance compounds synthesized by enantioselective protonation, (S)‐α‐damascone, (R)‐muscone, and (S,S)‐Vulcanolide are the most prominent ones. (S)‐α‐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)‐α‐damascone in 91% yield and with 71% ee.