Electron spin resonance study of radicals obtained from the oxidation of naturally occurring hydroxypyrones

Abstract

Many hydroxylated derivatives of γ-pyrone such as kojic acid, maltol, flavones, and also coumarins, may be oxidised by Ce^IV in acidic solutions to give radicals analogous to phenoxyl radicals. These have been observed by e.s.r. spectroscopy: the patterns of coupling constants obey some simple rules which are given in terms of non-bonding orbital coefficients. Addition of ·OH to 4-hydroxy-6-methylpyran-2-one gives a novel type of radical, 2,3,4-trihydroxy-6-methylpyranyl, whose structure is confirmed theoretically.