Chiral Synthesis of (R)-(+)-Citronellal via Stereoselective Protonation

Abstract
Protonation of the enolates (8) and (12) generated from an epimeric mixture of the .alpha.,.gamma.-disubstituted .gamma.-lactone (7) is shown to yield the syn-.alpha./.gamma.-disubstituted .gamma.-lactone (10) predominant over the anti-.alpha./.gamma.-disubstituted .gamma.-lactone (11). When the silyl enol ether (12) generated in situ is protonated with trifluoroacetic acid, the best selectivity is obtained. The syn-spimer (10) thus obtained is converted into (R)-(+)-citronellal (17) in four steps of reactions.
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