Synthesis of Alkynyl‐Glycinols by Lewis Acid Catalyzed Propargylic Substitution of Bis‐Imidates

Abstract

AbstractRacemic and enantioenriched alkynyl‐glycinols can be synthesized by Lewis acid catalyzed cyclization reaction of bis‐trichloracetimidates derived from alkynyl‐glycols. The cyclization proceeds selectively to give 4‐alkynyl‐oxazolines as the propargylic substitution products. Enantioenriched bis‐imidates that contain an alkyl or trimethylsilyl substituent at the acetylene gave oxazolines with complete inversion of configuration. In turn, considerable racemization was observed in the cyclization of bis‐imidates that contain a phenyl substituent. The racemization for these substrates can be suppressed by introduction of the electronegative substituent at the phenyl ring. Oxazolines prepared by bis‐imidate cyclization reaction can be readily transformed to protected alkynyl‐glycol derivatives.