Synthesis of 1,4-Benzodiazepine-3,5-diones

Even though benzodiazepines have a strong position in medicinal chemistry, very few synthetic
routes to 1H-1,4-benzodiazepine-3,5(2H,4H)-diones have ever been published and the claimed
products have often been poorly characterized. Through the present work several 1H-1,4-benzodiazepine-3,5(2H,4H)-diones have become available from N-carbamoylmethylanthranilic acids.
The required ring closures were achieved only when the amino groups of the starting materials
were substituted with electron withdrawing groups such as acetyl, alkyloxycarbonyl, or nitroso.
During the synthetic work a novel ring contraction rearrangement from a 1-nitroso-1H-1,4-benzodiazepine-3,5(2H,4H)-dione to a 3H-quinazoline-4-one was observed. The proposed mechanism
involves elimination of HNO followed by a proton-mediated loss of CO. The 1-nitrosated
1,4-benzodiazepinediones could be separately denitrosated to the corresponding amino compounds.