Carboxylic acids, from primary cycloaddition

The Meyer reaction is generally not of rtujor synthetic significarwe. It is observed when a nitro compound is exposed to strong acid. In diis way, carboxylic acids are obtained from primary nitro compounds. The reaction is thought to involve nitrile oxides and hydroxamic acids (RCONHOH) as intermediates. The latter can be isolated by avoiding heat, and the former have been trapped by 1,3-di-polar cycloaddition to alkenes and alkynes. ... 

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>. 

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