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42.11.6 Method 6: Acylation and Kinetic Resolution of Alcohols

DOI: 10.1055/sos-SD-042-00507

Methot, J. L.; Roush, W. R.Science of Synthesis, (200942495.

Whereas the majority of nucleophilic phosphine-catalyzed reactions involve 1,4-addition to activated alkenes, phosphines will also undergo 1,2-addition reactions with carbonyl compounds. The activity of tributylphosphine as a catalyst for the acylation of alcohols by carboxylic acid anhydrides is similar to that of 4-(dimethylamino)pyridine.[‌112‌,‌113‌] The reagent combinations acetic anhydride/tributylphosphine or benzoic anhydride/tributylphosphine can acylate a variety of alcohols, including menthol, hindered phenols, and tertiary alcohols. The probable mechanistic pathway involves nucleophilic activation of the anhydride to give an ion pair [Bu3P+COR1][R1CO2]. The rate of acylation decreases in the order tributylphosphine > diethyl(phenyl)phosphine > ethyl(diphenyl)phosphine, whereas tributylphosphine oxide and trimethyl phosphite are unreactive. Tributylphosphine can be easily removed from the reaction mixture by extraction with dilute mineral acids or by filtration chromatography.

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