Selective phosphorylation on primary alcohols of unprotected polyols

The triad tribenzylphosphite-iodine-pyridine offers a general selective met hod for phosphorylation reactions, of primary alcohols of unprotected alpha -diols and polyols, A mechanistic study by P-31 NMR allowed to evidence th e formation, from iododibenzyl phosphate and pyridine, of a very reactive p yridinium 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 dibenzylphosphori c esters. Under mild conditions, the cleavage of benzyl groups gives, monoe ster phosphoric acid.