Stereoelectronic effects in hydrogen-atom transfer reactions of substituted cyclohexyl radicals

Abstract

Thermolysis of the peroxyoxalates (1)–(7) and the diacyl peroxides (8)–(11) in cyclohexane at 100 °C gives cycloalkenes and cycloalkanes by hydrogen-atom transfer reactions of the initially formed conformationally biased 4-t-butyl-, 4-t-butyl-cis,cis-2,6-dimethyl-, 4-t-butyl-cis,trans-2,6-dimethyl-, 4-t-butyl-cis-2-methyl-, 4-t-butyl-trans-2-methyl-, and 5-t-butyl-cis-2-methylcyclohexyl radicals (12)–(17). The composition of the product mixtures indicates that transfer of axial β-hydrogen atoms occurs more rapidly than does transfer of equatorial β-hydrogen atoms. These results support the hypothesis that homolytic fission of a C–H bond is favoured when it lies close to the plane of an adjacent semi-occupied orbital.