A highly selective monoalkylation of tert-butyl 3,4-dihydroxy-4-phenylpiperidine-1-carboxylate under phase transfer conditions

Liquid–liquid phase transfer conditions have been found to provide highly selective monoalkylation of tert-butyl 3,4-dihydroxy-4-phenylpiperidine-1-carboxylate, a transformation for which many other common alkylation protocols proved inadequate. The high preference for 3-O-alkylation in the phase transfer alkylation is emphasised by the absence of diether formation even in the presence of a large excess of reagents.