Controlling chemoselective transformations of 4-acylpyridines via a Pd-C catalytic hydrodechlorination-hydrogenation

A novel Pd-C catalytic hydrodechlorination-hydrogenation was developed for a multi-step one-pot transformation of 4-acylpyridines. Under the selected conditions, 4-benzoylpyridines and 4-alkanoylpyridines were chemoselectively converted into the corresponding 4-benzylpiperidine hydrochlorides and α-alkyl-4-piperidinemethanol hydrochlorides, respectively. This catalytic method was performed simply by an addition of 1 equiv of ClCH2CHCl2 to the conventional hydrogenation system and directly gave the crystalline piperidine hydrochlorides in practical quantitative yields.