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Synthetic Applications of Enantioselective Protonation and Case Study for ( S )‐ α ‐Damascone
Author(s) -
Fehr Charles,
Randall Harvey
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.200890106
Subject(s) - chemistry , protonation , enantioselective synthesis , magnesium , lithium (medication) , enol , yield (engineering) , acetic acid , organic chemistry , catalysis , materials science , metallurgy , endocrinology , medicine , ion
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.