The preparation of (S)-3,4-dehydroproline from (2S,4R)-4-hydroxyproline

Abstract
(2S,4R)-N-Benzyloxycarbonyl-4-tosyloxyproline methyl ester, readily prepared from commercially available (2S,4R)-N-benzyl-oxycarbonyl-4-hydroxyproline, was converted to (S)-3,4-dehydroproline of high enantiomeric purity by a process which involved a highly regioselective phenylselenoxide elimination to introduce the olefinic function.