Pyrimidine Derivatives and Related Compounds II: Synthesis of some derivatives of pyrimido[1,2:2′,3′]pyrazolo[1,5‐a]pyrimidines, a new ring system

Abstract 3,5‐Diamino‐4‐phenylazo‐pyrazoles (1a–1c) react with acetylacetone and with ethyl acetoacetate to yield the corresponding pyrazolo[1,5‐a]pyrimidine derivatives 2a–2c and 3a–3c, respectively. Whereas 1a–1c add readily to methyl acrylate yielding the 4,5,6,7‐tetrahydropyrazolo[1,5‐a]‐pyrimidine derivatives 5a–5c, 1a–1c add to methylacrylonitrile or methyl methacrylate only under drastic conditions to yield 5d–5f. The pyrimido[1,2:2′,3′]pyrazolo[1,5‐a]pyrimidine derivatives 10a–10c are prepared by the action of acrylonitrile on 2a–2c. Compounds 10a–10c are readily converted into the corresponding oxo derivatives 12a–12c on treatment with acetic acid‐hydrochloric acid mixture.