A new method of N-benzhydryl deprotection in 2-azetidinone series

A mild and efficient procedure for the selective cleavage of N-benzhydryl protecting group of beta-lactams is described. The protected 2-azetidinones 4, precursors of carbapenems, were treated with a stoichiometric amount of N-bromosuccinimide and a catalytic amount of bromine under sun light irradiation in CH2Cl2-H2O mixture at 20 degreesC for 3 hours. The N-benzhydrol intermediates 6, which could be isolated, were then hydrolyzed with p-TsOH in aqueous acetone to furnish beta-lactams 7 and benzophenone quantitatively.