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

Abstract

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-β-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-β-d-glucofuranose and 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-d-glucopyranose, respectively.