RADICAL-MEDIATED BROMINATIONS AT RING POSITIONS OF CARBOHYDRATES

This chapter analyzes radical-mediated brominations at the ring positions of carbohydrates. The radical-mediated bromination reactions of carbohydrate compounds are, in appropriate circumstances, selective and efficient processes, but several criteria must be met for these advantages to be claimed: appropriate substituent groups must be used and various electronic and stereochemical needs must be satisfied. The radical-mediated brominations of carbohydrate derivatives have usually been conducted in refluxing carbon tetrachloride under tungsten (150–250 W) or heat (250–450 W) lamp, with either N-bromosuccinimide (1.2–5 molar equivalents) or bromine (2–5 equivalents) as the source of halogen. The addition of bromotrichloromethane to the carbon tetrachloride can be advantageous. Substrate concentrations have ranged from 0.02 to 0.2 mol l–1 and have depended to some degree on solubility factors, and ordinary laboratory glassware has mostly been used. This chapter analyzes the reaction conditions and suitable compounds associated with radical-mediated brominations and discuses the region- and stereochemistry of the reactions. It also explains the reactions of the bromine-containing products. © 1991 Academic Press Inc.