Single-Electron Transfer Pathways

The reaction of trimethylstannylsodium with two geminal dihalides, 6,6-dichloro-5,5-dimethyl-1-hexene and 6,6-diiodo-5,5-dimethyl-l-hexene, gave evidence of a single electron transfer pathway. An initial electron transfer from MetSn- to the geminal dihalides leads to the haloradical (X ), which then serves as the precursor to all the reactions and products detailed in Scheme 37195. 

The results obtained in the case of primary halides were confirmed by kinetic studies of their reactions with stannylanions using a stopped flow technique. The resulting rate constants were much greater than those calculated for an electron transfer according to the Hush-Marcus theory which supports a nucleophihc reactivity rather than a single electron transfer pathway. ... 

A cyclopentadienide ion can also be prepared by reaction of a diene with BU4NI via a single-electron transfer pathway [104] (Figure 4.43). 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

Oxidation of Carbon Skeletons with IBX. Allylic and benzylic positions are also susceptible to oxidation by IBX. These applications are not limited to the oxidation of compounds containing a pre-existing oxygen functionality but oxidize the hydrocarbon center directly to aldehydes or ketones. These oxidations also proceed via a single-electron-transfer pathway. The oxidation of aryl methyl groups to aryl aldehydes is accomplished with 3 equiv of IBX in DMSO or DMSO/fluorobenzene mixtures at 80-90 The first two equivalents of IBX initiate the single-electron-transfer to generate a benzylic carbocation. Subsequently, the reaction with water affords the alcohol in situ and the third equivalent of IBX completes the conversion to the desired benzaldehyde (eq 13). ... 

Initially, this field was pioneered by Li who reported in 2007 on the formation of new carbon-carbon bonds directly starting from diarylmethanes and 1,3-dicarbonyl compounds under mild reaction conditions (80-100 °C, 5-36 h) in the presence of catalytic quantities of an inexpensive iron precursor (iron(ii) chloride, 20 mol%) and stoichiometric quantities of an oxidant (DTBP). The overall reaction can be regarded as an iron(ii) chloride-catalysed oxidative activation of a benzylic carbon-hydrogen bond followed by a cross-coupling reaction to form a carbon-carbon bond (Scheme 13.7, bottom). The mechanistic proposal is based on a single-electron transfer pathway as shown in Scheme 13.7. Initial homolysis of DTBP in the presence of the iron(ii) salt forms both tert-butoxyl radical and an iron(iii) species. Then, proton abstraction from the diarenemethane generates the two key... 

Copper-catalysed aerobic oxidations (Scheme 2) implicating multiple possible mechanisms ranging from single-electron-transfer pathways to the involvement of organometallic intermediates and supported by recent smdies were discussed in a review article. ... 

Some of the advantages of copper catalysts are that they are inexpensive, abundant etc. In 2013, Fu, Peters and their co-workers reported a copper-catalyzed coupling of aryl halides with thiols via a single-electron transfer pathway. In order to prove the reaction mechanism, they performed the reaction of allyl-o-iodophenol with thiophenol as well. No cyclized product could be produced when the reactions were performed in the dark, while 57% of dihydrobenzofuran was formed when hv was introduced (Scheme 2.40). 

The direct oxidation of methane and alkanes by very strong oxidants aecording to a single electron-transfer pathway is followed by deprotonation of the extremely acidic radical cationic species RH ... 

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