Beneficial effect of internal hydrogen bonding interactions on the beta-fragmentation of primary alkoxyl radicals. Two-step conversion of D-xylo- and D-ribofuranoses into L-threose and D-erythrose, respectively.

Primary alkoxyl free radicals were generated from their readily synthesized N-phthalimido derivatives under reductive conditions. Primary alkoxyl radicals derived from their corresponding xylo- and ribofuranose derivatives underwent, exclusively, an unusual beta-fragmentation affording L-threose and D-erythrose derivatives, respectively. This occurs because the alkoxyl radical is capable of achieving an internal hydrogen-bonding interaction leading to a stable six-membered ring intramolecular hydrogen-bonded structure. When the hydroxyl group is protected, the beta-fragmentation pathway is prevented and the hydrogen atom transfer (HAT) pathway occurs. Computational studies provided strong support for the experimental observations.