Radical-trapping reagents, organic

Trialkyltin hydrides are common reagents in organic radical chemistry, but the toxic by-products are extremely difficult to remove from reaction products. To facilitate their removal, a pyrene-functionalized tin hydride has been prepared (entry 20) 25 After standard solution-phase radical reactions with the stannane, filtration through activated carbon traps the tin species to afford pure products. 

TEMPO is widely used as a radical trap, as a structural probe for biological systems in conjunction with EPR spectroscopy, as a reagent in organic synthesis, and as a mediator in controlled free radical polymerisation. As well as alcohol oxidation, TEMPO also finds use in the oxidation of other functional groups, including amines, phosphines, phenols, anilines, sulfides and organometallic compounds [144]. 

The reduction of alkylazides by single electron transfer (SET) cleanly furnishes the alkyl-aminyl radicals plus molecular nitrogen. A variety of metal reagents and photochemical methods exist. The reaction can also be performed with organic radicals, which add to the azide and release dinitrogen, too (see also Section 8.3.2). The resulting aminyl radical can be simply reduced to the corresponding amine or can further react with radical traps (olefins) to form C-N bonds. 

The radical produced from the oxidative decarboxylation may also be trapped intramolecularly to form five- and six-membered rings (Scheme 17). The Kolbe protocol avoids the use of the toxic organ-otin reagents that are commonly used in the formation of radicals. Moreover, when alkyltin hydride reagents are used, a C—H bond is formed. The Kolbe reaction protocol, on the other hand, allows the radical formed after cyclization to be captured by a different radical in a coelectrolysis experiment, rather than being reduced. This tandem sequence of events has been exploited in the construction of prostaglandin precursor (70) [37-41]. Here, the cyclized... 

For the purpose of arriving at polymeric reagents the formation of a carbon-carbon bond via radical means was desired. Trapping radicals in this way has been well known to modern organic chemists25. However, our problem in modifying PCTFE by this method was the heterogeneity of the polymer. In the solid state, PCTFE may be excluded from a solution-mediated reaction, and recovered unreacted. 

Selective trapping of alkyl radicals from the alkyl halide component during the course of the catalytic disproportionation is the same as the previous observation with silver, and it indicates that the prime source of radicals in the Kharasch reaction lies in the oxidative addition of alkyl halide to reduced iron in Equation 47. Separate pathways for reaction of i-propyl groups derived from the organic halide and the Grignard reagent are also supported by deuterium labelling studies which show that they are not completely equilibrated.(49) Furthermore, the observation of CIDNP (AE multiplet effect) In the labelled propane and propene... 

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