Ultrasound and ZnCl2 promoted synthesis of phthaloyl derivatives of alpha-amino carboxamides

A new, one-step and racemization-free synthesis of phthaloyl derivatives of -amino carboxamides is described. Under ultrasound. alpha -amino carboxami des and dipeptide derivatives react with monomethyl phthalate in the presen ce of BOP, ZnCl2 and i-Pr2NEt to afford the corresponding N-alpha-phthaloyl alpha -amino carboxamides or dipeptides in good to excellent yields. Cycli zation of the intermediate N-alpha-[(o-methoxycarbonyl)benzoyl]amino carbox amides to the desired products was very slow when the reaction was conducte d either in the absence of ZnCl2 and/or without sonication, but the process was greatly accelerated when both ZnCl2 and ultrasound were used.