BROMINATION OF 1,5-ANHYDROHEX-1-ENITOLS (GLYCALS) USING QUATERNARY AMMONIUM TRIBROMIDES AS BROMINE DONORS - SYNTHESIS OF ALPHA-1,2-TRANS-2-BROMO-2-DEOXYGLYCOPYRANOSYL BROMIDES AND FLUORIDES

Addition of bromine to glycals using quaternary ammonium tribromides a s bromine donors is realized with higher stereoselectivities (alpha-1, 2-trans configurated products) compared to bromination with molecular bromine. The reaction is neither sensitive to the solvent nor to the n ature of the protecting groups (acetyl, benzoyl, benzyl) of the glycal s and very slightly affected by the orientation of the substituents of the different glycals. Some of the alpha-1,2-trans dibromo adducts ha ve been isolated in 60-75 % yields and transformed into the correspond ing alpha-1,2-trans-2-bromo-2-deoxyglycopyranosyl fluorides.