Abstract
A versatile and chemoselective intramolecular oxa-Michael reaction of alpha,beta-unsaturated ester tethered on a prebuilt stereodefined beta-lactam ring in a novel synthesis of a bicyclic scaffold of 1,4 -oxazepane embedded on the beta-lactam ring has been developed. The tandem process involves a successive deprotection of the O-isopropylidene group, followed by the chemoselective nucleophilic conjugate addition of 2 degrees hydroxy functionalities of vic diol to the unsaturated esters preferentially 7-exo-trig mode of ring closure. The developed protocol proceeded well under mild alkaline conditions and furnished a novel scaffold of bicyclic beta-lactam featuring 1,4-oxazepane rings in a high chemoselective fashion.