Lactone-derived carbon-centered radicals: Formation and reactivity with oxygen

[GRAPHICS] Several lactones were examined to test the reactivity of carbon-centered ra dicals toward oxygen. Notably, the radical derived from 2-coumaranone (4) i s unreactive toward oxygen, while 2-cuomaranone itself shows enhanced react ivity toward hydrogen abstraction by alkoxyl radicals. We propose that five parameters influence diminished reactivity toward oxygen, i.e., (a) benzyl ic resonance stabilization, (b) unpaired spin delocalization on oxygen, (c) favorable stereoelectronic effects, (d) electron-withdrawing effects, and (e) steric effects.