The hydroxyacetylpiperidines and their N‐benzyl derivatives. The 2‐hydroxymethyl‐2‐piperidyl‐ and 2‐hydroxymethyl‐2‐pyridyl‐1,3‐dioxolanes

Abstract

The hydroxyacetylpiperidines, their ethylene ketals, and the N‐benzyl derivatives of these new piperidines have been synthesized. Methylolation of 2‐(2‐ and 4‐pyridyl)‐1,3‐dioxolanes by heating with paraformaldehyde at 185° led to 2‐hydroxymethyl‐2‐(2‐ and 4‐pyridyl)‐i,3‐dioxolanes (7,8, respectively). 2‐Hydroxymethyl‐2‐(3‐pyridyl)‐1,3‐dioxolane (13) was obtained by reaction of 2‐bromomethyl‐2‐(3‐pyridyl)‐1,3‐dioxolane with aqueous sodium hydroxide at 190°. Hydrogenation of these pyridine ketals with rhodium‐charcoal catalyst produced the corresponding piperidine ketals (16,17,18). Acid hydrolysis of the piperidine ketals and their N‐benzyl derivatives led to the hydroxyacetylpiperidines (1,2,3) and their N‐benzyl derivatives (25,26,27). The N‐benzylhydroxyacetylpiperidines undergo rapid hydrogenolysis with palladium‐charcoal catalyst to produce the hydroxyacetylpiperidines. Further hydrogenation produces the piperidyl‐1,2‐ethanediols. The hydroxyacetylpiperidines are somewhat unstable, hygroscopic substances which polymerize with dehydration on standing; in solution they are relatively stable. Their N‐benzyl, ketal, and hydrochloride salt derivatives, on the other hand, represent stable, synthetically useful intermediates from which the reactive trifunctional hydroxyacetylpiperidines may readily be prepared.