Hypohalites alkoxy radicals from

Hypohalites IRO-Hal) are similar to nitrates (see p. 155 in their photochemical behaviour. Ultraviolet irradiation gives an (n,Ji > excited state that cleaves to form an alkoxy radical and a halogen atom. The radical may undergo alpha-cleavage before recombination with the halogen atom occurs, and this accounts for the formation of 5-iodopentanal (5.69) from the hypoiodite of cydopentanol such hypoiodites are generated in situ from the alcohol. Iodine and merturyfll oxide. In open-chain systems the alkoxy radical can... 

Alkoxy radicals for ring expansion can be generated from alcohols by oxidative methods such as hypohalite thermolysis/photolysis [19a] and lead tetraacetate oxidation [19b], or peroxide reduction [19c]. The recent development of the hyper-valent organoiodine reagent (diacetoxyiodo)benzene (DIB) provides another way for efficient generation of alkoxy radicals (Scheme 11) [19d]. Additional oxidative methods to prepare cyclopropyloxy radicals include reaction of tertiary cyclopropanols or their silyl ether derivatives with various reagents such as manganese(III) tris(pyridine-2-carboxylate) [Mn(pic)3] [20a], Fe(III) salts [20b], and vanadyl ace-tylacetate [20c] (Scheme 12). 

The photolysis of a tertiary hypohalite (readily prepared from the corresponding alcohol) generates alkoxy radical, which abstracts hydrogen from 5-carbon to produce an alkyl radical. The resulting alkyl radical abstracts halogen atom from a second molecule of the hypohalite to give 5-haloalcohol, which is cyclized in presence of a base to form a tetrahydrofuran derivative [9]. These reactions are very similar to the Barton reaction and proceed through a six-membered cyclic transition... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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