Highly Selective Acylation of Alcohols Using Enol Esters Catalyzed by Iminophosphoranes

The iminophosphorane bases PhCH2NP(MeNCH2CH2)3N and PhCH2NP(NMe2)3 catalyze the acylation of primary alcohols with enol esters in excellent yields and in high selectivity. It was found that acid labile groups such as acetal and epoxide survive under the reaction conditions. Groups such as TBS and disulfide, which undergo cleavage in the presence of Ac2O and the Lewis acid Sc(OTf)3, are also unaffected. Diene, conjugated acetylene, oxazoline, nitro, and benzodioxane groups are also compatible with our catalyst/reagent system. Because secondary alcohols do not react under our conditions, our methodology is attractive for the selective acylation of primary alcohols. Polymer-supported iminophosphorane catalysts are also shown to be useful in these reactions, thus opening the possibility of wider applications.