Reductive fragmentation of carbohydrate anomeric alkoxy radicals. Synthesis of alditols with potential utility as chiral synthons

A series of anomeric nitrate esters and N-phthalimido glycosides of carbohydrates in furanose and pyranose forms have been synthesized in order to generate the corresponding alkoxy radicals and study the C1-C2 fragmentation reaction under reductive conditions. This reaction constitutes a two-step method for the transformation of carbohydrates into the corresponding alditols with one less carbon. Using this methodology, interesting four- and five-carbon building blocks for natural products synthesis possessing D-erythritol, D-threitol, D-xylitol, and D-arabinitol stereochemistry have been prepared. The synthesis of 1,2-O-isopropylidene-beta-L-threose (40) and 1-acetamido-2,4,5-tri-O-acetyl-D-arabinitol (50) have also been achieved from 1,2:5,6-di-O-isopropylidene-beta-D-glucofuranose and 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-D-glucopyranose, respectively.