Photobromination of carbohydrate derivatives. Part 5. Preparation and reactions of (5S)-1,2,3,4-tetra-O-acetyl-5-bromo-β-D-xylopyranose; a new type of ‘double-headed’ nucleoside

Abstract

Photobromination of tetra-O-acetyl-β-D-xylopyranose gives a crystalline product (2) with bromine replacing the axial hydrogen atom at C-5. Nucleophilic displacement of the bromine afforded compounds with inverted stereochemistry at this centre, the methoxy-product (9) undergoing displacement of acetoxy-group from C-1 on treatment with hydrogen bromide and giving the 5-methoxyglycosyl bromide ester (10). Elimination reactions of the bromides (2) and (10) were studied, and the derived ‘glycal’ compounds (3) and (12) afford routes to 4-deoxy-L-threo-pentose and its enantiomer, respectively. Attempts to prepare new types of crown ethers by way of a di-O-glycosylethane-1,2-diol derivative (15) were not successful, but a novel type of ‘double-headed’ nucleoside (22) was obtained from the initial bromide (2).