A high performance oxidation method for secondary alcohols by inductive activation of TEMPO in combination with pyridine-bromine complexes

A new TEMPO-mediated catalytic oxidation method in combination with Py·HBr3 (stoichiometric) is developed for oxidation of secondary alcohols to the corresponding ketones. The performance of this oxidizing system is better compared with that of TEMPO method combined with R4NBr3. Poly(4-vinylpyridine)·HBr3 can be used in place of Py·HBr3. The electron-withdrawing substituent at the C-4 position of TEMPO increases the reactivity of TEMPO significantly in the oxidation of electron-deficient alcohols such as polyhaloalkylmethanols. Inductive effect of the substituent of TEMPO is discussed through the characterization of the redox potential of N-O radical by cyclic voltammetry.

A combination of Py·HBr3 as a co-oxidant and the electronically activated TEMPO as a recyclable catalyst is useful for oxidation of not only common alcohols, but also of the electron-deficient secondary alcohols such as ArCH(OH)CFCl2.