Systemic Fungicides. The Synthesis of Pyrazolo[1,5- a ]pyrimidine Analogues of Carboxin

The synthesis of a series of pyrazolo [1,5-a] pyrimidine derivatives, structural analogues of the systemic fungicide carboxin, is described. A common intermediate incorporating structural features desirable for fungicidal activity, N-phenyl-3(5)-amino-5(3)-methylpyrazole-4- carboxamide (6), was used to prepare pyrazolo [1,5-a] pyrimidines variously substituted in positions 5 and 7 of the ring system. Bromination of N-phenyl-2-methylpyrazolo[1,5-a]pyrimidine-3-carboxamide (8) occurred preferentially in the phenyl ring and the 6-bromo derivative was prepared by bromination of the corresponding 3-ethoxycarbonyl derivative (24). Attempted nitration of the ester (24) resulted in displacement of the ethoxycarbonyl substituent by a nitro group. The simplest pyrazolo [1,5-a] pyrimidine (8) showed a high level of fungicidal acitvity in fungal growth assays of Basidiomycete species, but compounds substituted in the pyrimidine ring were inactive.