Reactions of nitric oxide and nitrogen dioxide with functionalised alkenes and dienes

Pure nitric oxide does not add to alkenes containing acceptor or donor substituents, or to conjugated dienes, to afford beta-nitrosoalkyl radicals. EPR spectra show that reactions are initiated by NO2 addition to carbon-carbon double bonds to produce beta-nitroalkyl radicals which combine with nitric oxide to yield beta-nitro-nitroso-compounds. The latter trap other radicals to afford mixtures of aminoxyl radicals and, where possible, the nitroso-compounds tautomerise to oximes which oxidise to iminoxyl radicals. EPR spectra obtained on reaction of NO-NO2 mixtures with 2,5-dimethylhexa-2,4-diene have shown the presence of a di-tert-alkylaminoxyl plus a tert,sec-dialkylaminoxyl, providing good support for this mechanism. Product analyses have established that 2-oxo-4-methylpent-3-ene and 1-acetylcyclohexene undergo extensive oxidative degradation. For enol ethers, reaction with NO-NO2 leads to hydrolysis giving the corresponding carbonyl compound and alcohol, followed by ketal and ester formation.