A Mechanistic Study of the Photoreactions of Deoxy Iodo Sugars

Article abstract of DOI:10.1021/jo00205a027

Quantum yields of 0.31, 3.7, and 1.1 have been determined for the photochemical disappearance in heptane of 6-deoxy-6-iodo-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (1), 3-deoxy-3-iodo-1,2:5,6-di-O-isopropylidene-α-D-allofuranose (2), and 3-deoxy-3-iodo-1,2:3,4-di-O-isopropylidene-α-D-glucofuranose (3), respectively.The major reaction for compounds 2 and 3 is epimerization at C-3, a reaction not observable for compound 1.Photochemical epimerization takes place in at least two ways.First, carbon-iodine bond homolysis followed by recombination of the radicalsproduced either regenerates the starting iodide or gives its C-3 epimer.Second, a chain reaction takes place in which the propagation step involves transfer of an iodine atom from the deoxy iodo sugar (2 or 3) to the carbon radical produced by carbon-iodine bond homolysis.In the presence of oxygen a new set of photoproducts is formed.These include enol esters, alcohols, and carbonyl compounds.