The cyclization of 4-amino-1,3-dimethyl-1H-pyrazole-5-carbonitrile (I) or 4-amino-1,3-dimethyl-1H-pyrazole-5-carboxamide (II) with acetic anhydride and H2O2 or NaOH gives 1,3,5-trimethyl-6,7-dihydro-1H-pyrazolo[4,5-d]pyrimidin-7-one (III), which by reaction with POCl3/PCl3 is converted into 7-chloro-1,3,5-trimethyl-6,7-dihydro-1H-pyrazolo[4,5-d]pyrimidine (IV). The reaction of (IV) with 2-ethylaziridine (V) affords 7-(2-ethylaziridin-1-yl)-1,3,5-trimethyl-6,7-dihydro-1H-pyrazolo[4,5-d]pyrimidine (VI), which is finally rearranged to the tricyclic target compound by means of NaI in acetone.
The reaction of 1,3-dimethyl-4,5-dihydro-1H-pyrazol-5-one (I) with POCl3 followed by nitration with HNO3 gives 5-chloro-1,3-dimethyl-4-nitro-1H-pyrazole (II), which is treated with KCN to yield 1,3-dimethyl-4-nitro-1H-pyrazole-5-carbonitrile (III). The cyclization of (III) with butane-1,2-diamine (IV) by means of Ts-OH affords the imidazoline (V), which is acylated with acetic anhydride to provide the 1-acetyl imidazoline (VI). Finally, this compound is cyclized by reduction of its NO2 group followed by heating.