Addition of halogenoazides to glycals

Abstract Addition of chloroazide to 3,4,6-tri- O -acetyl-1,5-anhydro-2-deoxy- d - lyxo - ( 1 ) and - d - arabino -hex-1-enitol ( 2 ) under u.v. irradiation proceeds regio- and stereo-selectively yielding mainly O -acetyl derivatives of 2-azido-2-deoxy- d -galactopyranose and - d -glucopyranose, respectively. 3,4,6-Tri- O -acetyl-2-chloro-2-deoxy-α- d -galactopyranosyl azide and 3,4,6-tri- O -acetyl-2-azido-2-deoxy-α- d -talopyranose (from 1 ), and 1,3,4,6-tetra- O -acetyl-2-chloro-2-deoxy-α- d -glucopyranosyl azide and 1,3,4,6-tetra- O -acetyl-2-azido-2-deoxy-α- d -mannopyranose (from 2 ) are byproducts. 1,5-Anhydro-3,4,6-tri- O -benzyl-2-deoxy- d - lyxo - and - d - arabino -hex-1-enitol reacted more rapidly with chloroazide, to give, under irradiation, derivatives of 2-azido-2-deoxy- d -galactose and - d -glucose, respectively. However, reaction in the dark gave mainly O -benzyl derivatives of 2-chloro-2-deoxy-α- d -galacto- and -α- d -glucopyranosyl azide. The difference between the products obtained may depend on the existence of two parallel processes, one radical (under irradiation), and the other ionic (reaction in the dark).