Remarkable dependence of the regioselectivity of free radical additions to 3-cinnamoyloxazolidin-2-ones on the stability of the intermediate adduct-radical, electrophilicity of the adding radicals and the conditions for their generation

Abstract

Electrophilic (CCl₃) and nucleophilic radicals (Prⁱ) are found to add at 80 °C to the CC bond of 3-(E)-cinnamoyl-4-phenyloxazolidin-2-one 1a and 3-(E)-cinnamoyl-4-benzyloxazolidin-2-one 1b predominantly at the α-position of the bond. While for the CCl₃ radical no product of β-addition has been found, for the Prⁱ radical such a path constitutes up to 40% of the whole process at 80 °C. An interplay between the stability of the intermediate adduct radicals and the electrophilicity or nucleophilicity of the radicals undergoing addition are invoked to rationalize the observation. At a low temperature (–23 °C) β-addition of the Prⁱ radical becomes the dominant process (up to 75%).