Oxidation of α-Trifluoromethyl and Nonfluorinated Secondary Alcohols to Ketones Using a Nitroxide Catalyst

A methodology for the oxidation of α-trifluoromethyl alcohols to the corresponding trifluoromethyl ketones is presented. A catalytic quantity of a nitroxide is used, and potassium persulfate serves as the terminal oxidant. The methodology proves effective for aromatic, heteroaromatic, and conjugated alcohol substrates. It can be extended to nonfluorinated secondary alcohols and, in this case, can be applied to a range of aromatic, heteroaromatic, and aliphatic alcohols.

Scale-up of Sodium Persulfate Mediated, Nitroxide Catalyzed Oxidative Functionalization Reactions

BACKGROUND

Oxidation is a valuable tool in preparative organic chemistry. Oxoammonium salts and nitroxides have proven valuable as reagents and catalysts in this endeavor.

OBJECTIVE

The objective of this study is to scale up the oxidative amidation, ester formation, and nitrile formation using nitroxide as an organocatalyst.

METHODS

Oxidative functionalization reactions were scaled from the 1 mmol to the 1 mole level. Sodium persulfate was used as the primary oxidant, and a nitroxide was employed as a catalyst. The products of the reactions were isolated in analytically pure form by extraction with no need for column chromatography.

RESULTS

The oxidative amidation and esterification of aldehydes can be scaled up from 1 mmol to 1 mole effectively, with comparable product yields being obtained at each increment. This work shows that conditions developed on a small scale can be transferred to a larger scale without reoptimization. The oxidative functionalization of aldehydes to prepare nitriles is not amenable to direct scale-up due to the concomitant formation of significant quantities of the corresponding carboxylic acid, thereby compromising the product yield.

CONCLUSION

Two of the three oxidative transformations studied here can be scaled up successfully from the 1 mmol to the 1 mole level.