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-beta-D-glucopyranosyl)piperidine (44.1%), N-(2,4,6-tri-O-b enzoyl-beta-D-glucopyranosyl)piperidine (1.5%), N-benzoylpiperidine and pip eridinium benzoate (approx 1 mol of each of these two products per mol of s ubstrate). When several penta-O-benzoyl-D-glucopyranoses containing selecti vely C-14-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 benzo yloxy groups originally attached to C-3, C-4, and C-6 remain in the major p roduct of the reaction. These results demonstrate that the first compound p roduced in the reaction is N-(3,4,6-tri-O-benzoyl-beta-D-glucopyranosyl)pip eridine which could not be isolated because it undergoes two consecutive be nzoyl migrations: a migration from O-3 to O-2 to give the 2,4,6-tri-O-benzo ate, followed by a migration from O-4 to O-3 to afford the 2,3,6-tri-O-benz oate. A mechanism to explain the formation of piperidinium benzoate from be nzoyloxy-C-2 of penta-O-benzoyl-D-glucopyranose is proposed. (C) 1999 Elsev ier Science Ltd. All rights reserved.