A facile method for the synthesis of novel fluorinated pyrido [2′,3′:3,4] pyrazolo [1,5-a] pyrimidines

The reaction of 3-amino-4-trifluoromethyl-6-substituted pyrazolo [3,4-b] pyridines (1) with active methylene compounds, such as ethoxy methylene malononitrile, ethyl-(ethoxymethylene)cyanoacetate and 1,3-diketones gave exclusively pyrido [2′,3′:3,4] pyrazolo [1,5-a] pyrimidines (2) and (5), respectively in high yields. When compound (1) was reacted with ethoxy methylene diethyl malonate (EMME), intermediate 3-amino (methylenediethylmalonate)-4-trifluoromethyl-6-substituted pyrazolo [3,4-b] pyridines (3) are obtained. The intermediates are further cyclized to give product (4).