Regioselective synthesis of 6-trifluoromethyl-1,4,5,6-tetrahydropyrazolo[3,4-b]pyran derivatives

A facile two-step procedure for the synthesis of 6-(trifluoromethyl)-1,4,5,6-tetrahydropyrazolo[3,4-b]pyran derivatives (4) from the reaction of 4-arylidene-3-methyl-1-phenyl-5-pyrazolones (1) with ethyl trifluoroacetoacetate (2), a versatile fluorinated building-block, was presented. Furthermore, to increase the efficiency of this reaction, the more convenient one-pot three-component process was also developed with a slightly lower yield. Treatment of 4 with P2O5, conc. H2SO4, POCl3/Py or p-TsOH under the drastic conditions did not afford the corresponding dehydrated products.