(a) 1,3,8-Trimethyl-4-phenyl-5,6,7,8-tetrahydropyrazolo[3,4-b][1,5]diazepine-
1H ,4H-5,7-dione:
23 g (0.1 mole) of 4-benzene-azo-1,3-dimethyl-5-methylaminopyrazole are
hydrogenated in 250 ml of ethanol with 60 g of Raney nickel, at 60°C; a
hydrogen pressure of 50 atmospheres. When the uptake of hydrogen has
ended, the catalyst is filtered off and the reaction solution is evaporated in
vacuum. The residue is triturated with ether/petroleum ether and the
precipitate of 4-amino-1,3-dimethyl-5-methylaminopyrazole is filtered off. The
product is sufficiently pure for the subsequent reactions. MP: 87°C.
(b) 4-α-Ethoxycarbonylacetylamino-1,3-dimethyl-5-methylaminopyrazole:
1.4 g (0.01 mole) of 4-amino-1,3-dimethyl-5-methylaminopyrazole are
dissolved in 20 ml of toluene, 1 ml (0.012 mole) of monomethyl malonate
chloride is slowly added dropwise, whilst cooling with ice, and the mixture is
subsequently stirred at room temperature for one hour. The toluene is
stripped off in vacuum, the residue is taken up in chloroform and the mixture
is washed with ice-cold NaHCO 3 solution and water and dried with Na 2 SO 4 .
After evaporating off the solvent, 4-α-ethoxycarbonylacetylamino-1,3-
dimethyl-5-methylaminopyrazole remains as an yellowish oil.
(c) 1,3,8-Trimethyl-5,6,7,8-tetrahydropyrazolo[3,4-b][1,5]diazepine-1H,4H-5,7-dione:
15 ml of a 1 molar sodium methanolate solution are added to 2.4 g (0.01
mole) of 4-α-ethoxycarbonylacetylamino-1,3-dimethyl-5-methyl-
aminopyrazole, dissolved in 100 ml of ethanol, and the mixture is stirred at
room temperature for 8 hours. It is then neutralized with alcoholic HCl and
evaporated in vacuum, the residue is taken up in CHCl 3 , the mixture is filtered
and the filtrate is again evaporated. After adding ether to the residue, the
latter becomes crystalline and can be filtered off. It is recrystallized from
isopropanol/diisopropyl ether. MP: 202°C.
(d) 1,3,8-Trimethyl-4-phenyl-5,6,7,8-tetrahydropyrazolo[3,4-b][1,5]diazepine-
1H,4H-5,7-dione:
A mixture of 1 g of 1,3,8-trimethyl-5,6,7,8-tetrahydropyrazolo[3,4-
b][1,5]diazepine-1H,4H-5,7-dione, 1 g of potassium acetate and 1.5 g of
copper powder in 100 ml of bromobenzene is boiled under reflux, whilst
stirring, until the reaction has ended (monitoring by thin layer
chromatography, 3-4 hours). The mixture is then allowed to cool to room
temperature and is diluted with CH 2 Cl 2 (200 ml), the inorganic constituents
are filtered off, the organic phase is washed with water and dried and the
solvent is stripped off in vacuum. Recrystallization of the residue from
diisopropyl ether gives the analytically pure 1,3,8-trimethyl-4-phenyl-5,6,7,8-
tetrahydropyrazolo[3,4-b][1,5]diazepine-1H,4H-5,7-dione. MP: 168°C.
