SELECTIVE PHOSPHORYLATION ON PRIMARY ALCOHOLS OF UNPROTECTED POLYOLS

Abstract The triad tribenzylphosphite-iodine-pyridine offers a general selective method for phosphorylation reactions of primary alcohols of unprotected α-diols and polyols. A mechanistic study by 31P NMR allowed to evidence the formation, from iododibenzyl phosphate and pyridine, of a very reactive pyridinium salt intermediate. This analysis shows that pyridine behaves as a covalent catalyst like DMAP in acylation reactions from acylchloride. Due to its steric hindrance and high reactivity, this species appears to be the efficient selective phosphorylation reagent but leads to dibenzylphosphoric esters. Under mild conditions, the cleavage of benzyl groups gives monoester phosphoric acid.