Preparation method of stable isotope labeled diazepam

The invention discloses a preparation method of stable isotope labeled diazepam, which comprises the following steps: step 1, taking 4-chloroacetanilide as an initial raw material, and reacting with benzoic anhydride to obtain 2-acetamido-5-chlorobenzophenone; step 2, enabling the 2-acetamido-5-chlorobenzophenone to react with hydrochloric acid, so as to generate 2-amino-5-chlorobenzophenone; step 3, enabling the 2-amino-5-chlorobenzophenone to react with glycine ethyl ester hydrochloride, so as to generate 7-chloro-1, 3-dihydro-5-phenyl-2H-1, 4-benzodiazepine-2-ketone, and enabling the 7-chloro-1, 3-dihydro-5-phenyl-2H-1, 4-benzodiazepine-2-ketone to react with glycine ethyl ester hydrochloride so as to generate 7-chloro-1, 3-dihydro-5-phenyl-2H-1, 4 4, the 7-chloro-1, 3-dihydro-5-phenyl-2H-1, 4-benzodiazepam and a methylation reagent are subjected to a reaction under the liquid phase alkaline condition, and the stable isotope labeled diazepam is generated; wherein benzoic anhydride and/or a methylation reag