3.5 g of 4-chloroacetyl-1,3-dimethyl-1,4,9,10-tetrahydropyrazolo[4,3-
b][1,5]benzodiazepin-10-one, 8.1 g of N-methylpiperazine and 50 ml of
toluene are stirred at 80°C for 2 h. 60 ml of dilute sodium bicarbonate
solution are added to the mixture, the layers are separated and the aqueous
phase is extracted by shaking it with toluene several times more before
concentrating it to dryness in vacuum. The residue is stirred with 100 ml of
isopropanol and is filtered; the filtrate is concentrated in vacuum. The residue
(4.0 g) is purified by stirring it with diethyl ether and by recrystallizing it from
toluene, which yields 2.2 g of 1,3-dimethyl-4-[(4-methylpiperazin-1-yl)acetyl]-1,4,9,10-tetrahydropyrazolo[4,3-b][1,5]benzodiazepin-10-one, melting point
186-188°C.
