The reaction of penta-O-benzoyl-d-glucopyranose with piperidine: characterization of the products isolated and study of the reaction mechanism

The reaction of penta-O-benzoyl-d-glucopyranose with piperidine gave N-(2,3,6-tri-O-benzoyl-β-d-glucopyranosyl)piperidine (44.1%), N-(2,4,6-tri-O-benzoyl-β-d-glucopyranosyl)piperidine (1.5%), N-benzoylpiperidine and piperidinium benzoate (approx 1 mol of each of these two products per mol of substrate). When several penta-O-benzoyl-d-glucopyranoses containing selectively 14C-labeled benzoyloxy groups were submitted to the same reaction, it was found that N-benzoylpiperidine is formed at the expense of benzoyloxy-C-1, piperidinium benzoate arises mainly from benzoyloxy-C-2, and the benzoyloxy groups originally attached to C-3, C-4, and C-6 remain in the major product of the reaction. These results demonstrate that the first compound produced in the reaction is N-(3,4,6-tri-O-benzoyl-β-d-glucopyranosyl)piperidine, which could not be isolated because it undergoes two consecutive benzoyl migrations: a migration from O-3 to O-2 to give the 2,4,6-tri-O-benzoate, followed by a migration from O-4 to O-3 to afford the 2,3,6-tri-O-benzoate. A mechanism to explain the formation of piperidinium benzoate from benzoyloxy-C-2 of penta-O-benzoyl-d-glucopyranose is proposed.