A convenient synthesis of medium-sized lactams through RCM reaction of oxyoxazolidinones

Oxyoxazolidinones, which are prepared from secondary O-acylmandelamides by treatment with TBSOTf, underwent the RCM reaction in the presence of Grubbs catalyst to give oxazoloazepines or oxazoloazecines, which were readily converted into N-unsubstituted seven-membered or eight-membered lactams by the reductive treatment.