Alkoxyl radical, reaction with nitric oxide

The Barton nitrite ester photolysis is undeniably one of the most popular and useful reactions in radical chemistry for the functionalization of remote and inactivated positions within steroids (Scheme 19). Photolysis of nitrite esters gives nitric oxide and an alkoxyl radical that abstracts an ideally positioned hydrogen atom (1,5-hydrogen atom abstraction). The resulting alkyl radical reacts with nitric oxide in a solvent cage to afford the nitroso-alcohol derivative that is finally isolated as an oxime [53]. Related cyclizations of alkoxyl radicals have been reported by Surzur photolysis of y,(5-alkenyl nitrite esters leads to alkoxyl radicals that undergo subsequent tandem 5-exo cyclization followed by NO-trapping [54, 55]. 

Alkyl nitrates and alkyl nitrites can be formed by the reaction of alkoxyl radicals (RO ) with nitrogen dioxide and nitric oxide, respectively ... 

As mentioned earlier, when NO concentration exceeds that of superoxide, nitric oxide mostly exhibits an inhibitory effect on lipid peroxidation, reacting with lipid peroxyl radicals. These reactions are now well studied [42-44]. The simplest suggestion could be the participation of NO in termination reaction with peroxyl radicals. However, it was found that NO reacts with at least two radicals during inhibition of lipid peroxidation [50]. On these grounds it was proposed that LOONO, a product of the NO recombination with peroxyl radical LOO is rapidly decomposed to LO and N02 and the second NO reacts with LO to form nitroso ester of fatty acid (Reaction (7), Figure 25.1). Alkoxyl radical LO may be transformed into a nitro epoxy compound after rearrangement (Reaction (8)). In addition, LOONO may be hydrolyzed to form fatty acid hydroperoxide (Reaction (6)). Various nitrated lipids can also be formed in the reactions of peroxynitrite and other NO metabolites. 

The photolysis of organic nitrites of appropriate constitution and conformation in solvents such as benzene or acetonitrile transforms them into A-nitroso alcohols via the sequence (1) a homolytic fission of the O-N bond of their nitrosoxy group (2) an intramolecular d-hydrogen abstraction of the resulting alkoxyl radicals to generate a d-carbon radical and (3) formation of d-nitroso alcohols by combining of the d-carbon radical with the generated nitric oxide. The nitroso alcohols are isolated as d-hydroxyimino alcohols as a result of spontaneous thermal isomerization or as nitroso-dimers [1] (Scheme 1). This transformation has been named the Barton reaction [2, 3],... 

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