A comprehensive picture of the one-electron oxidation chemistry of enols,enolates and a-carbonyl radicals: oxidation potentials and characterizationof radical intermediates

摘要

Oxidation potentials of 40 enols, enolates and some selected a-carbonyl radicals are presented alongwith their characterization by various techniques as applicable (X-ray, EPR, ENDOR, general TRIPLE,magnetic susceptibility measurements, UV-vis, fast scan cyclic voltammetry, isotope effects). The modelcompounds comprise representatives of stable simple enols linked to a multitude of substituents (alkyl,alkenyl, alkynyl, aryl, heteroaryl, propargyl alcohols) and of stable simple enols of amides. The resultsallow to clarify the primary reaction pathway of enol radical cations as a rapid deprotonation and—ifwarranted by the redox potential and the strength of the oxidant—a follow-up oxidation of the resultanta-carbonyl radical to the a-carbonyl cation. Moreover, the experimental oxidation potentials were lin-early correlated with AM1 computed ionization potentials after correction for solvation. The correlationallows a reliable prediction of oxidation potentials of radicals including a-carbonyl radicals. After com-puting redox potentials of relevant radicals, the possibility of one-electron transfer between enolates andflavin and the involvement of various radicals of ascorbic acid in oxidation processes were assessed.