Extraction with ethyl acetate or ether and distillation of the crude furnishes pure (2). As shown in the reaction scheme, the overall reaction proceeds via several unisolated intermediates and it has not yet been established whether the cyclization occurs with (la) or ( 1 b). Remarkably, in the present synthesis, ring closure takes place in alkaline solution whereas comparable cyclizations invariably have to be performed in acidic medial2, 51. Like other aminoazoles having a 2-aminopyrrole structure, compound (2) reacts with 1,3dicarbonyl compounds to give pyrazolo[2,3-a]pyrimidines (3)'6'.
3(5)-Aminopyrazole (2)
Hydrazine hydrate (55g, 1.1 mol) is added to a solution of K 2 C 0 3 (140g, 1 mol) in water (400ml). To this vigorously stirred mixture is then added dropwise 2-chloroacrylonitrile1'J (87.5 g, 1 mol) at 5-10°C (ice-salt cooling) under nitrogen over a period of 1 h. Stirring is continued for 1 h at room temperature and 1.5h at 4O-5O0C, and the mixture left to stand overnight. Extraction for 24 h with ethyl acetate"] and vacuum distillation of the residual crude oil (75 g, 90°/,) under nitrogen affords 58g (70%) of ( 2 ) , b. p. 120-122"C/0.3 torr. Compound (2) solidifies on cooling, preferably with seeding (m.p. 36°C). The IR spectrum accords with that of authentic 3(5)-aminopyra~ole[~~. Picrate : m. p. 222 "C from methanol.