Peculiarities of cyclization of ethyl 2-ethoxymethylene-3-oxo-3-(polyfluoroalkyl)propionates with 3-amino-5-hydroxypyrazole

The reactions of ethyl 2-ethoxymethylene-3-oxo-3-(polyfluoroalkyl)propionates with 3-amino-5-hydroxypyrazole result in ethyl 2,7-dihydroxy-7-(polyfluoroalkyl)-4,7-dihydropyrazolo[1,5-a]pyrimidin-6-carboxylates under mild conditions. These products undergo recyclization in refluxing ethanol to form ethyl 3-hydroxy-4-(polyfluoroalkyl)-1H-pyrazolo[3,4-b]pyridin-5-carboxylates, whereas in refluxing glacial acetic acid they are dehydrated to ethyl 2-hydroxy-7-(polyfluoroalkyl)pyrazolo[1,5-a]pyrimidin-6-carboxylates. The non-fluorinated ethyl 2-ethoxymethylene-3-oxo esters in the reactions with 3-amino-5-hydroxypyrazole in ethanol (or glacial acetic acid) under reflux form only ethyl 2-hydroxy-7-phenyl(hydroxy)pyrazolo[1,5-a]pyrimidin-6-carboxylates.

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► Ethyl 2-ethoxymethylene-3-oxo-3-(polyfluoroalkyl)propionates react with 3-amino-5-hydroxypyrazole to give dihydropyrazolo[1,5-a]pyrimidines.
► Dihydropyrazolo[1,5-a]pyrimidines undergo recyclization to form pyrazolo[3,4-b]pyridines and are dehydrated to pyrazolo[1,5-a]pyrimidines.
► Non-fluorinated 2-ethoxymethylene-3-oxo esters in the reactions with 3-amino-5-hydroxypyrazole form only pyrazolo[1,5-a]pyrimidines.