Abstract New synthesis of 11-acyl-5, 11-dihydro-6H-pyrido [2, 3-b][1, 4] benzodiazepin-6- ones (42-44) is reported. The crucial steps (Scheme VI) represented N-oxydation of 1 (1A) to 35 (35A), facilitated ring-closure of 36 into 37, its subsequent N-α-chloroacetylation to 38, aminolysis to 39-41 (involving NO anchimeric assistance as depicted in 38A) and deoxygenation to 42-44 (Scheme VII). The central intermediate 37 is also obtained on ...