Tributyl- or triphenylphosphine promotes a one-pot, three-step method for the synthesis
of differently substituted dibenzodiazepinones from N-aryl-2-nitroanilines. Pyridine analogues and the corresponding thiazepinones can
also be formed using this method. The process involves deoxygenation of the nitro
group, then formation of an iminophosphorane intermediate and its intramolecular condensation
with a carboxyl group placed in the N-aryl group. The role of the carboxyl group in the formation of the iminophosphorane
and the mode of cyclization are discussed.
Key words
cyclocondensation - reduction - nitro compounds - dibenzodiazepines - regioselectivity