Application of a thermal rearrangement reaction to questions of structure of condensed dihydrodiazepinones: Synthesis and characterization of isomeric dihydropyrido[3,4‐b] [1,4]diazepinones from 3,4‐diaminopyridine and ethyl acetoacetate

Abstract

AbstractReaction of ethyl acetoacetate with 3,4‐diaminopyridine can theoretically give rise to the iso‐meric dihydrodiazepinones 1 and 3. However, only one of these (compound 1) was formed on direct condensation of the reactants in boiling toluene. The preparation of 3 required the synthesis of the pyridylaminocrotonate 2, which cyclized under conditions of base catalysis. When subjected to dry fusion, both diazepine derivatives rearranged to give isomeric isopropenylpyridoimidazol‐ones. The structures of these rearranged products were used to characterize the diazepines from which they were derived, according to a technique previously described (20,21). Our results contradict a recent report (17) ascribing structure 3 to the product from 3,4‐diaminopyridine and ethyl acetoacetate in boiling xylene.