Tandem Conjugate Addition-Cyclization Synthesis of 1,5-Benzodiazepines

Abstract

Reported is the synthesis of 1,5-benzodiazepines by the reaction of readily available phenylenediamines with ethyl propiolate. The process is very simple and metal-free, involving refluxing the starting materials in methanol for the requisite time. Different solvents were tested, with methylene chloride and ethanol affording similar yields but requiring longer reaction times. The overall yields were mostly very good, but unsymmetrical diamines afforded mixtures of regioisomers. The substrate scope was also poorly studied in terms of the propiolate reactant.