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

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 14 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-alpha-D-glucofuranose with 13 or 16 gave 6-bromo-6-de-oxy-1.2:3.5-di-O-isopropylidene-alpha-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-alpha-D-allofuranose derivatives and a new procedure for selective O-formylation are described.