Synthesis of chiral 1,5-disubstituted pyrrolidinones via electrophile-induced cyclization of 2-(3-butenyl)oxazolines derived from (1R,2S)- and (1S,2R)-norephedrine

摘要

Starting from (1R,2S)- and (1S,2R)-norephedrine, enantiomers of the corresponding 2-(3-butenyl)oxazolines were prepared in a two-step process. The cyclization of the intermediate alkenylamides with phenylselenyl bromide afforded cyclic imidates instead of the expected pyrrolidinones. The electrophile-induced cyclizations of 2-alkenyloxazolines with bromine or iodine produced diastereomeric mixtures of chiral 1,5-disubstituted pyrrolidinones. The ring closure of the all-cis (I R,2S,5R)-diastereomer 7 with NaH resulted in the tetrahydropyrrolo[2, 1-b]oxazol-5-one derivative 18, which was alternatively prepared by the cyclocondensation of (I R,2S)-norephedrine with levulinic acid. (c) 2006 Published by Elsevier Ltd.