A suspension of 45.0 g. of 2-carbethoxy-N-(benzyloxycarbonyl)glycine in 120 ml. of dry methylene chloride, cooled to -20° C., is treated portionwise with 30 g. of phosphorus pentachloride and stirred for 30 minutes at -20° C. to -10° C. To the now clear solution, there is added at the same temperature a solution of 27.7 g. of 2-amino-4-chlorobenzophenone and 1 ml. of dimethylformamide in 120 ml. of dry methylene chloride. The mixture is concentrated under reduced pressure at 40°-45° C. The residue is partitioned between methylene chloride and 10% aqueous soda solution and the methylene chloride phase is dried over sodium sulfate and evaporated to dryness. There is obtained a reddish-colored resin of crude 2'-benzoyl-2-[(benzyloxycarbonyl)amino]-2-carbethoxy-5'-chloroacetanilide, which is then immediately reacted with 130 ml. of a 33% solution of hydrobromic acid in glacial acetic acid. After stirring at room temperature for 90 minutes, the obtained solution is concentrated at 45° C. and the oily residue partitioned between water and ether. The aqueous solution is made weakly alkaline with solid sodium bicarbonate while cooling with ice. The separated base is extracted with methylene chloride and the extracts are dried over sodium sulfate and evaporated to dryness. The resulting oil is dissolved in a mixture of 180 ml. of toluene and 180 ml. of glacial acetic acid and heated at 80° C. for 90 minutes. The solution is concentrated to an oil and is crystallized from ether so that there is obtained 8-chloro-2,3-dihydro-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-carboxylic acid ethyl ester, having a melting point of 214°-217° C. (decomposition). Recrystallization from acetonitrile does not increase the melting point.
