Various halomethyleniminium salts as novel Vilsmeier agents were synthesized from formamide or N-methylformamide with POCl3. Treatment of N-1-substituted-aminopyrazoles including N-1-phenyl-5-aminopyrazoles, N-1-(2-pyridinyl)-5-aminopyrazoles, and N-1-(2- quinolinyl)-5-aminopyrazoles with these agents gave the corresponding pyrazolo [3, 4-d] pyrimidine, N-(1H-pyrazol-5-yl) formamide, or N-(1H-pyrazol-5-yl) formamidine. The ...