Oxidative hydrogen migration

Periana and coworkers have recently made computational studies with respect to the mechanism of regioselective hydroarylation of alkenes reported by Periana, Matsumoto, and coworkcrs- " induced by the Ph-Ir(acac)2L catalyst in the formation of ethylbenzene. Iridium inserts into the benzene C-H bond, resulting in an oxidative hydrogen migration through transition... 

Whereas exo-norbornene oxide rearranges to nortricyclanol on treatment with strong base through transannular C-H insertion (Scheme 5.11), endo-norbornene oxide 64 gives norcamphor 65 as the major product (Scheme 5.14) [15, 22]. This product arises from 1,2-hydrogen migration very little transannular rearrangement is observed. These two reaction pathways are often found to be in competition with one another, and subtle differences in substrate structure, and even in the base employed, can have a profound influence on product distribution. 

The 2,3-substituted indols are formed via a palladium-catalyzed coupling reaction of aryl halide, o-alkenylphenyl isocyanide, and amine (Equation (122)).481 Oxidative addition of an aryl halide, insertion of both the isonitrile and alkene moieties of o-alkenylphenyl isocyanide, and 1,3-hydrogen migration may form a 7r-allylpalladium species, which is then attacked by an amine to afford an indol. 

TPR of supported bimetallic catalysts often reveals whether the two metals are in contact or not. The TPR pattern of the 1 1 FeRh/SiOi catalyst in Fig. 2.4 shows that the bimetallic combination reduces largely in the same temperature range as the rhodium catalyst does, indicating that rhodium catalyzes the reduction of the less noble iron. This forms evidence that rhodium and iron are well mixed in the fresh catalyst. The reduction mechanism is as follows. As soon as rhodium becomes metallic it causes hydrogen to dissociate atomic hydrogen migrates to iron oxide in contact with metallic rhodium and reduces the oxide instantaneously. 

Subsequent one-electron transfer and intramolecular hydrogen migration lead to radical 102 followed by reaction with 02 to yield hydroperoxide radical 103. Radical 103 is further oxidized to a dihydroperoxide (104), which decomposes to anthra-quinone. Alternatively, 103 may be transformed to a diradical that eventually gives anthracene as a byproduct. The ratio of the two products strongly depends on the solvent used. The highest yield of anthraquinone (85% at 100% conversion) was achieved in 95% aqueous pyridine. 

A one-step synthesis of isochromene itself has been reported from indene oxide (191) (66CC415). Irradiation of the epoxide in benzene affords two products, isochromene and indan-2-one, in similar quantities. It was proposed that initial fission of the carbon-carbon bond of the three-membered ring is followed by 1,4- or 1,2-hydrogen migration (Scheme 36). 

The CS2 and COS-based ligands are all dealt with in Section 16.4.3. Dimeric oxidation products of the heteroallyls and other ligands in which a CS2 or COS fragment is found are treated briefly in Section 16.4.4. No further attention is paid to ligands like S—S—Me and methanedithiolate or dithioacetal, which occurs for example in the reaction of two moles of (4) with one mole of CS2 in a two-step hydrogen migration.6... 

The formation of a carboxylic acid from Baeyer-Villiger oxidation of an aldehyde requires hydrogen migration. 

How can one use this thermochemical effect for a preparative route to enol radical cation intermediates in solution Since one usually has to start with the ketone tautomer, two possibilities are conceivable at first from Fig. 2 (1) direct oxidation of the ketone to the ketone radical cation followed by a 1,3-hydrogen migration to provide the enol radical cation, or (2) selective one-electron oxidation of the enol that is present in the equilibrium situation under fast enolization conditions. 

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