Conversion of hydroxyl groups into bromo groups in carbohydrates with inversion of configuration

Abstract

A novel reagent system is described for the efficient, one-step transformation of hydroxyl groups in carbohydrates to bromodeoxy groups. The reaction proceeds with inversion of configuration. The reagent system consists of triphenylphosphine, tribromoimidazole, and imidazole in toluene at elevated temperature. The carbohydrate need not be soluble in toluene. The examples given include substitution of isolated primary and secondary hydroxyl groups in otherwise protected carbohydrates as well as disubstitution involving one primary and one secondary position in hexopyranosides. High yields are obtained in the replacement of hydroxyl by bromine in the 2-position of 3,4,6-protected methyl α-D-gluco- and -mannopyranosides.