Pyrazolopyridine carboxylic acids

Scheme 15 Synthesis of positional isomers of pyrazolopyridine carboxylic acid derivatives...

A convenient one-step transformation of primary and secondary amines into the corresponding unprotected guanidines using 4-benzyl-3,5-dimethyl-l/f-pyrazole-l-carboxamidine 90 and its polymer-bound variant were described <06S461>. 1,3-Dipolar cycloaddition of polymer-bound alkynes to azomethine imines generated in situ from N-aminopyridine iodides followed by aromatization of the cycloadducts gave polymer-bound pyrazolopyridines that were released from the resin as carboxylic acids with trifluoroacetic acid or as methyl esters with sodium methoxide <06JCO344>. 

Pyrazolopyridines were synthesized from various resin-bound alkynes and azomethine imines generated in situ in solution (Scheme 11.20). Ester-linked products were cleaved with trifluoroacetic acid or sodium methoxide, and the products were obtained as carboxylic acids or methyl esters, respectively. 

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