The mechanism of the hydroxyl → halogen exchange reaction in the presence of triphenylphosphine, N-bromosuccinimide, and N,N-dimethylformamide: Application of a new Vilsmeier-type reagent in carbohydrate chemistry

Article abstract of DOI:10.1016/0008-6215(92)84042-Q

Triphenylphosphine reacts with N-bromosuccinimide to give a phosphonium salt (13), which reacts with N,N-dimethylformamide to afford N,N-dimethylsuccinimidomethaniminium bromide (16). The latter product reacts with an alcohol to give an O-formiminium compound 17, and, in the presence of an alcohol, 13 is transformed into an alkoxyphosphonium intermediate (14). Both 4 and 17 can be converted by heating into an alkyl bromide. Hydrolysis of 17 gives the corresponding O-formyl derivative. Reaction of 1.2:5.6-di-O-isopropylidene-α-D-glucofuranose with 13 or 16 gave 6-bromo-6-deoxy-1,2:3,5-di-O-isopropylidene-α-D-glucofuranose and a possible mechanism for these reactions is suggested. An efficient method for the preparation of 3-deoxy-3-halogeno-1,2:5,6-di-O-isopropylidene-α-D-allofuranose derivatives and a new procedure for selective O-formylation are described.