The condensation of 6-(2-chlorophenyl)-1,2-dihydro-8-nitro-1H,4H-imidazo[1,2-a][1,4]benzodiazepin-1-one (I) with 1-(dimethoxymethyl)-4-methylpiperazine (II) gives the free base of loprazolam (III), which is then treated with methanesulfonic acid.
The reaction of 5-(2-chlorophenyl)-7-nitro-3H-1,4-benzodiazepin-2-thione (I) with glycine (A) by means of Na2CO3 in refluxing ethanol-water gives 2-carboxymethylamino-7-nitro-5-(2-chlorophenyl)-3H-1,4-benzodiazepine (II), which is cyclized by means of dicyclohexylcarbodiimide in methylene chloride to afford 8-nitro-(2-chlorophenyl)-1,2-dihydro-1H,4H-imidazo[1,2-a][1,4]benzodiazepin-1-one (III). The reaction of (III) with dimethylformamide diethylacetal (B) by means of triethylamine in benzene yields 8-nitro-2-(dimethylaminomethylene)-6-(2-chlorophenyl)-1,2-dihydro-1H,4H-imidazo[1,2a][1,4]benzodiazepin-1-one (IV), which is treated with N-methylpiperazine (C) in refluxing toluene to produce 8-nitro-(2-chlorophenyl)-2-(N-methylpiperazin-1-ylmethylene)-1,2-dihydro-1H,4H-imidazo [1,2-a][1,4]benzodiazepin-1-one (V). This compound is finally treated with methanesulfonic acid.