 It selectively activates the carboxylic acid to give the carboxymethyleneammonium salt, which can be reduced by a mild reductant like lithium tris("t"-butoxy)aluminum hydride to afford an aldehyde in a one pot procedure.This procedure is known to tolerate reactive carbonyl functionalities such as ketone as well as moderately reactive ester, olefin, nitrile, and halide moieties.The carboxyl radical, •COOH, only exists briefly.