The reaction of 2-phenyl -4- aryl -2,3 -dihydro- 1,5- benzodiazepine with ethyl diazoacetate using power Cu as a catlyst gives a normal cycloaddition product, azirino-benzodiazepine (I), and an unprecedent product pyrro - benzodiazepine (II). The yield of (II) was increased to 50% under the optimum condition.From the reaction mechanism, which involved formation of benzodiazepinium ethoxycarbonylmethylate (V), the reaction mechanism, which involved formation of benzodiazepinium ethoxycarbonyl- methylate (V) followed by cycloaddition reaction, was tentatively proposed. The reaction was proved to be stereospecific based on the analysis of X - ray and NMR spectra.

Key words: DIAZEPAM, ETHYL ACETATE P, DIAZO COMPOUNDS, COPPER, X-RAY DIFFRACTION ANALYSIS, NMR SPECTROMETRY, STEREOCHEMISTRY