Nitrogen-oxygen bonds homolysis

Relatively few studies of photorearrangements in five- and six-membered nitrogen-containing heterocycles have been reported. Isoxazole-to-oxazole photorearrangements have been employed in the syntheses of 2-(2-aryl-5-oxazolyl)benzoates, and nitrogen-oxygen bond homolysis appears to be the first step (as shown in Scheme 5) in the photorearrangement of the fused... 

The conversion of the benzohydroxamic acid (191) into the amide (192) is the result of nitrogen-oxygen bond homolysis.Photodecomposition of aminophenazone (193) in aqueous solution gave N-acetyl-N-methyl-N -phenylhydrazine (194), whereas on irradiation in acetone products arising by... 

The conversion of hydroxamic acids into the corresponding amides is believed to involve initial formation of amidyl radicals by nitrogen-oxygen bond homolysis. Photodecomposition of hydroperoxides, peroxides and ozonides has also been examined. 

Miscellaneous Reactions.- Excited state alkyl nitrites undergo competing nitrogen-oxygen bond homolysis and exchange by labelled... 

Nitrogen-oxygen bond homolysis competes with... 

Irradiation of non-8-enyl nitrite (126) leads via homolysis of the nitrogen-oxygen bond and 1,5-hydrogen transfer as shown in Scheme 7 to the acyclic and cyclic nitroso-alcohols... 

Photocyclization arising by intramolecular elimination of HC1, HBr, or HI has been extensively used in the synthesis of nitrogen-containing heterocycles, but much less so in oxygen and sulfur systems. The mechanism of these transformations is not always clear some proceed by way of an initial carbon-halogen bond homolysis, whereas others involve cyclization and... 

Anchimeric assistance by the aUcoxyl oxygen lone pair promotes heterolytic S v 1 and reactions at nitrogen as well as homolysis of the N—Cl bond. A-Haloamides are also amidyl radical sources" but their heterolytic reactivity is known to involve positive, rather than negative, halogen ... 

In this configuration, the alkoxyl oxygen lone-pair involvement promotes not only heterolytic Sjvl and 8 2 reactions at nitrogen and homolysis of the A—OAcyl bond, but molecular rearrangements. 

The first step in the mechanism is the homolysis of the 0-N bond to form an oxygen-centered radical and a nitrogen-centered free radical. Next, the highly reactive alkoxyl radical abstracts a hydrogen atom from the 5-position (5-position) via a quasi chair-like six-atom transition state to generate a new carbon-centered radical that is captured by the initially formed NO free radical. If a competing radical source such as iodine is present, the reaction leads to an iodohydrin, which can cyclize to form a tetrahydrofuran derivative. Occasionally, tetrahydropyran derivatives are obtained in low yields. 

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