Iminyl radicals in gas-phase synthesis. II. Formation of a-branched nitriles from cycloalkanone azines

Gas-phase pyrolysis of cyclopentanone and cyclohexanone azines results in the formation of iminyl radicals. These undergo ring cleavage to the ω-cyanoalkyl radicals, which stabilize, by internal hydrogen-atom transfer, to the corresponding α-cyanoalkyl radicals. Fragmentation of the latter yields acrylonitrile and alkyl radicals, which can recombine with the α-cyanoalkyl radicals to form α-alkylated nitriles. The mechanisms involved are discussed with reference to isotopic labellingstudies.