Bicyclization, peroxy radical

After bicyclic radical formation, 02 rapidly adds to the radical, forming a bicyclic peroxy radical, for example... 

Birdsall, A.W., Dreoni, J., Elrod, M.J. Investigation of the role of bicyclic peroxy radicals in the oxidation mechanism of toluene. J. Phys. Chem. A 114, 10655-10663 (2010)... 

Butanedione is formed in the oxidation of o-xylene via a bridged bicyclic peroxy radical, and is a co-product of butenedial and of 2,5(H)-furanone. It is also formed in the oxidation of methyl ethyl ketone under low to moderate NOx via peroxy-peroxy radical reactions. 

More recently, Bachi and coworkers extended and adapted the TOCO reaction to the synthesis of 2,3-dioxabicyclo[3.3.1]nonane derivatives hke 228 (Scheme 52) ° ° . As detailed in Scheme 53a, the bridged bicyclic hydroperoxide-endoperoxides hke 229 are obtained, from (S )-limonene (227), in a 4-component one-operation free-radical domino reaction in which 5 new bonds are sequentially formed. Particular experimental conditions are required in order to reduce the formation of by-products 230 and (PhS)2, and to favor the critical 6-exo-ring closure of peroxy-radical 231 to carbon-centered radical 232206 chemoselective reduction of bridged bicyclic hydroperoxide-endoperoxides... 

The peroxy radical formed in (Reaction 2b) is expected to cyclicize to form a corresponding bicyclic radical (Reaction 4) or react with nitric oxide via an abstraction mechanism to form the corresponding aromatic oxy radicals (Reaction 5a) ... 

Alkyl peroxy radicals generally react with NO to form alkoxy radicals (assuming sufficient NO is present). Aromatic peroxy radicals, in contrast, are believed to cyclicize, forming bicyclic radicals. For the product of reaction b above, the energetically favored bicyclic radical is... 

Interest in the chemistry and biochemistry of peroxides has been recently stimulated by the fact that the important class of natural products, the prostaglandins, has two members (PGG and PGH) that contain the peroxide linkage. Further, the proposed mechanism for the biosynthesis of these peroxides involves a novel peroxy radical bicyclization. Thus, one mechanism for biosynthesis of PGG, proposed in 1967 ( 1,, involves an autoxidative-... 

Addition of the PhOO radical to the ipso carbon of the phenyl ring has a low barrier (20 kcal mol below the entrance channel) and a tight transition state. This path is important and the addition results in a dioxirane cyclohexadienyl radical (Y(C6 )Y(C02). This bicyclic cyclohexadienyl-dioxirane adduct has resonance between the ortho and para positions on the ring. The formation path has a barrier of 29 kcal mol relatively to the stabilized peroxy... 

Suh, L, Zhang, R., Molina, L.T., Molina, M.J. Oxidation mechanism of aromatic peroxy and bicyclic radicals from OH-toluene reactions. J. Am. Chem. Soc. 125, 12655-12665 (2003)... 

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