Highly selective acylation of alcohols using enol esters catalyzed by iminophosphoranes

The iminophosphorane bases PhCH2N=P(MeNCH2CR2)(3)N and PhCH2N=P(NMe2)(3) ca talyze the acylation of primary alcohols with enol esters in excellent yiel ds and in high selectivity. It was found that acid labile groups such as ac etal 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, oxazoli ne, nitro, and benzodioxane groups are also compatible with our catalyst/re agent system. Because secondary alcohols do not react under our conditions, our methodology is attractive for the selective acylation of primary alcoh ols. Polymer-supported iminophosphorane catalysts are also shown to be usef ul in these reactions, thus opening the possibility of wider applications.