Synthesis of 2-fluorinated pyrazolo[1,5-a]pyridines via base- mediated [3+2] cycloaddition of N-aminopyridinium salts with gem-difluorostyrenes

Abstract

A method for the construction of 2-fluoropyrazolo[1,5-a]pyridines through base-promoted [3+2] cycloaddition of N-aminopyridinium salts with gem-difluorostyrenes has been established. A range of N-heterocycles with 2-fluorinated pyrazo[1,5-a]pyridines were efficiently obtained in moderate to good yields. The impact of different substituents on the reaction was discussed in detail. The protocol shows great potential for the synthesis of valuable fluorinated compounds by utilizing gem-difluorostyrenes as fluoride-containing building blocks.