A reaffirmation of stereoelectronic control in the alkaline hydrolysis of methyl and ethyl ethylene phosphate

Abstract

A reinvestigation of the product distribution in the hydrolysis of ethyl and methyl ethylene phosphates has confirmed our earlier suggestion (Taira , J. Org. Chem., 1984, 4531) that the stereoelectronic effect is an important factor in these reactions. In contrast to the claims of Kluger and Thatcher (J. Am. Chem. Soc., 1985, 107, 6006; J. Org. Chem., 1986, 51, 207), the increase in exocyclic cleavage product, methanol, with increasing strong base is shown to arise from an artifactual side-reaction in the base catalyzed hydrolysis of methyl ethylene phosphate. The initial product of endocyclic cleavage, methyl hydroxyethyl phosphate, reacts with a second molecule of methyl ethylene phosphate to yield a “triester” dimer which subsequently releases methanol to yield a “diester” dimer. Although a small amount of exocyclic cleavage product is observed in strong alkali (2 – 4% ± 1.5% for methyl ethylene phosphate and <. 5% ±1.5% for ethyl ethylene phosphate) the proportion does not vary with alkali when the hydrolysis reaction is run under dilute conditions to minimize the dimerization reaction. Even these small proportions of exocyclic cleavage are still completely consistent with arguments regarding stereoelectronic control in these reactions.