A phosphorus nuclear magnetic resonance spectroscopic study of the conversion of hydroxy groups into iodo groups in carbohydrates using the iodine–triphenylphosphine–imidazole reagent

Abstract

31 P N.m.r. spectroscopic studies on the mechanism of the reaction between 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose and the reagent system iodine–triphenylphosphine–imidazole are presented. Three different solvents were tested, toluene–acetonitrile (2:1), acetonitrile, and pyridine. A mechanism is proposed, which is largely consistent with that previously suggested. Imidazole may be replaced by triethylamine, and the reaction also proceeds in pyridine without imidazole or triethylamine. Some features of the equilibrium between triphenyldi-iodophosphorane and iodotriphenylphosphonium iodide (formed from iodine and triphenylphosphine) are also discussed.