N-Bromosuccinimide-Mediated Transformation of Acetylated 1,5-Anhydro-1-C-phenyl-d-hexitols

Abstract

Radical-mediated halogenation constitutes a valuable synthetic tool, in particular for achieving regio and stereocontrolled preparations of brominated or chlorinated sugar derivatives.¹ This chain reaction process involves, as the main steps, the initial homolytic cleavage of an activated C—H bond followed by trapping of the resulting carbon-centered radical with a halogenated species. For cyclic sugar derivatives, halogenation occurs either at C-1 or at C-4 (furanose series) or C-5 (pyranose series) depending on the substituents attached to these carbon atoms.¹ Moreover, trapping of the intermediate carbon-centered free radical occurs with a high stereoselectivity, so that substrates containing an activated C—H bond can be converted under mild conditions and in high yield into halogenated polyfunctional products which are not accessible by other routes. Our recent synthesis of a variety of bromoglycosyl imines² from glycosyl azides contitutes a new example of the synthetic value of this method.