Reaction between hydrazines and chiral α-acetylenic ketones: synthesis of novel enantiomerically pure pyrazolyl-β-amino alcohols

Abstract

A simple and efficient methodology toward the stereoselective synthesis of novel, enantiomerically pure, pyrazolyl-β-amino alcohols is presented. Thus, when hydrazines 4a, b were allowed to react at 0°C with chiral α-acetylenic ketones of type 3, pyrazolyl oxazolidine derivatives 5a– d were formed with total regioselectivity in 92–97% yield. Subsequent oxazolidine ring opening by means of TFA, and re-protection of the amino group as the N-Boc derivatives, afforded enantiopure amino alcohols 7a– d.