Free radical chain reactions involving an electron transfer process

Abstract

<p>Photostimulated reactions of 2-substituted-2-nitropropanes with 1°-alkoxide ions in alcohol solution afford 2,2-dialkoxypropanes in reasonable yields. The reactions are inhibited by O[subscript]2 and m-dinitrobenzene and do not occur in the dark. Furthermore, the reactions are retarded for a discrete period of time by a small amount of di-tert-butyl nitroxide. The evidence supports a free radical chain process involving the trapping of Me[subscript]2CNO[subscript]2[superscript]· by 1°-RO[superscript]-, the decomposition of ROCMe[subscript]2NO[subscript]2[superscript]-· to ROCMe[subscript]2[superscript]· and the oxidation of ROCM[subscript]2[superscript]· to ROCMe[subscript]2[superscript]+ by XCMe[subscript]2NO[subscript]2. The free radical chain process leading to the ketal is also inhibited by methyl vinyl ketone or (1-methoxyethenyl)benzene. The measured initial kinetic chain lengths for sodium methoxide and potassium methoxide with 2-bromo-2-nitropropane in methanol are 10 and 38, respectively. The initial kinetic chain lengths of 38 and 171 are measured for the reaction with sodium ethoxide and potassium ethoxide in ethanol, respectively. The relative reactivities of the 1°-alkoxide ions and the anion of 2-nitropropane in the photostimulated reaction with 2-bromo-2-nitropropane depend upon the counterions and the nature of solvents and are independent of the concentration of 2-bromo-2-nitropropane, the leaving group or of the initial ratio of (MeO[superscript]-) / (Me[subscript]2C=NO[subscript]2[superscript]-);The photostimulated reaction of [alpha],[beta]-unsaturated ketones with alkylmercury halides in the presence of iodide ion produce the conjugate addition products. The conjugate addition reaction is a free radical chain process possibly involving the RHgI[subscript]2[superscript]-. Several pieces of evidence including the relative reactivities of 2-cyclopentenone and 2-cyclohexenone, the stereochemistry of the alkylation of 5-methyl-2-cyclohexenone and the trapping of tert-butyl radical by 1,1-diphenylethylene, support the conclusion that the conjugate additions of (t-Bu)[subscript]2CuLi and (t-Bu)[subscript]3ZnLi to [alpha],[beta]-unsaturated ketones involve a free radical as an intermediate.</p>