The process of making benzodiazepine derivatives of the formula ##STR24## wherein R.sup.1 is hydrogen, methyl, ethyl, isopropyl, butyl, sec.-butyl, tert.-butyl, amyl, hexyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, benzyl or 2-chloroethyl,
- R.sup.2 is chloro or bromo,
- A and B are, independently of each other, unsubstituted or substituted by up to 2 substituents selected from the group consisting of nitro, trifluoromethyl, halogen, alkyl of up to 4 carbon atoms and alkoxy of up to 4 carbon atoms, or a pharmaceutically acceptable acid addition salt of said benzodiazepine derivative of formula I, the said process comprising
- A. subjecting an acyldiamine of the formula ##STR25## werein A, B and R.sup.1 have meaning as above, or an acid addition salt of said acyldiamine, at a temperature between 110.degree. and 130.degree. C to the action of a phosphorus oxyhalide as cyclization agent whereby a compound of the formula I is obtained, and B optionally converting said compound of formula I to a pharmaceutically acceptable acid addition salt thereof.