Halide-tolerant mediators

In contrast to Ag(I), the ions Ce(III), Co(II) and Fe(II) remain soluble in the presence of halide ions liberated during the destruction of halogenated organics. Thus Co(III) is a halide-tolerant mediator. Destruction rates greater than 3L/d have been achieved with EG. Treatability studies of Trimsol cutting oil contaminated with various radionuclides were discussed by Hickman et al. [306],... 

The development of the Grignard-type addition to carbonyl compounds mediated by transition metals would be of interest as the compatibility with a variety of functionality would be expected under the reaction conditions employed. One example has been reported on the addition of allyl halides to aldehydes in the presence of cobalt or nickel metal however, yields were low (up to 22%). Benzylic nickel halides prepared in situ by the oxidative addition of benzyl halides to metallic nickel were found to add to benzil and give the corresponding 3-hydroxyketones in high yields(46). The reaction appears to be quite general and will tolerate a wide range of functionality. 

The reaction products are the A -unprotected 2-stannylindoles 27, which are available for further manipulation through the Stille palladium-mediated coupling with aromatic or unsaturated halides or triflates. Since a very wide variety of functional groups are known to tolerate both radical and palladium-mediated reactions, this synthesis was an interesting innovation for the construction of 3- or... 

Photochemical methods are useful both for the preparation and the reaction of alkyl halides. In the former case, a convenient procedure obtains alcohol activation through a visible-light-mediated photocatalytic reaction. The procedure, based on the redox chemistry of Ru (bipy) complexes, was demonstrated to convert alcohols into the corresponding bromides and iodides in good yields and with exceptional functional group tolerance (see Scheme 26). ... 

Liu and Xu report a previously unprecedented reaction for Cu-catalyzed trifluoro-methylation of terminal alkenes via allylic C(sp —H bond activation. Advantages of this method over others, which involve the use of Pd-catalyzed stannane couplings or Cu-mediated nucleophilic trifluoromethylation of allyl halides, is the starting point of much simpler substrates and better functional group tolerance. The reaction can be conducted under mild conditions and exhibits good tolerance to moisture. Some examples are illustrated (Schane 7.10). 

Cross-Coupling Reactions. TASF(Et) activates vinyl-, alkynyl-, and allylsilanes in the Pd-mediated cross-coupling with vinyl and aryl iodides and bromides. As illustrated in eqs 8-10, the reaction is stereospecific and chemoselective. This crosscoupling protocol is remarkably tolerant towards a variety of other functional groups such as carbonyl, amino, hydroxy, and nitro. Vinylsilanes can be synthesized from hexamethyldisilane and vinyl iodides in the presence of TASF(Et) (eq 10) via cleavage of a Si-Si bond. Aryl iodides can also be synthesized by this method. TASF is superior to tetra-n-butylanunonium fluoride for these reactions. In the absence of a vinylsilane reagent, one of the methyl groups from the difluorotrimethylsilicate is substituted for the halide (eq 11). ... 

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