New Synthetic Bromination Procedures for use in Radiolabelling-Chemistry: Reaction of C-Metallated Derivatives of Carbohydrates with Bromide, in the Presence of Mild Oxidizing Agents

Article abstract of DOI:10.1002/hlca.19830660403

In the presence of 2 mol-equiv. of AcONa, both triglycosylborane 1 and dicyclohexylglycosylborane 2 readily react with bromine chloride generated in situ from bromide and N-chlorosuccinimide (NCS) to give the bromo-sugar 3 (75 and 60 percent, resp.).The use of the BH3-THF/bromide/NCS/2 AcONa procedure permits the rapid, face-specific synthesis of 6 (58percent uptake of bromine) and face-selective synthesis of 8/9 (71percent uptake of bromine), from vinyl ether derivatives 5 and 7, respectively.The dicyclohexylborane/bromide/NCS/2 AcONa procedure leads to the fast and quantitative conversion of 11 to the bromosugar 12 (91percent).Hydroboration-transmetallation sequences give access to C-mercuriated carbohydrates 13 (71percent) and 14 (78percent).The bis(glycosyl)mercury derivative 13 is spontaneously cleaved by reaction with one equivalent of bromide/chloramine-T/aqueous HCl-solution to give 3 (87percent) and 14 (76percent).Hydrostannylation of acetylenic sugar 15 gave the (E)-stannylvinyl derivative 16 as the major product.This latter precursor 16 is spontaneously cleaved by the bromide/chloramine-T/aqueous HCl-solution reagent to give the bromovinyl sugar-17 (96percent).