Stereoselective Synthesis of 5-(1-Hydroxyalkyl)-2-pyrrolidinones Utilizing Oxidation of 5-Alkylidene-2-pyrrolidinones to Acyliminium Ion Precursors

A general method was devised for the LiN(TMS)2/AgOTf (=2:1)-catalyzed intramolecular (5-exo-dig) cyclization of β-alkynylamides 1 possessing alkyl, aryl or no functional groups at the terminal alkynes, to 5-alkylidene-2-pyrrolidinones 2. These 5-alkylidene-2-pyrrolidinones were oxidized to the diol-type alkoxylactams 3 by dimethyldioxirane (DMD) or mCPBA in MeOH. These alkoxylactams are useful as tertiary N-acyliminium ion precursors for the synthesis of threo-5-(1-hydroxyalkyl)-2-pyrrolidinone derivatives 5.