Atom transfer radical equation

Another application of ruthenium indenylidene complexes was the atom transfer radical addition of carbon tetrachloride to vinyl monomers reported by Verpoort [61]. This Kharasch reaction afforded good yields for all substrates tested, especially with the catalyst VIII (Equation 8.11, Table 8.8). 

Intramolecular cyclization of the chiral oxime ether 993 in the presence of isopropyl iodide and triethylborane affords the 3,4,5-trisubstituted tetrahydropyran-2-one 994 in poor yield but with good diastereoselectivity (Equation 388) <2003JOG5618>. Similarly, a triethylborane-induced atom transfer radical cyclization of 3-butenyl 2-iodoacetate leads to 4-(iodomethyl)tetrahydropyran-2-one. Higher yields are achieved when conducting the reaction at lower concentrations (Equation 389) <2000JA11041 >. 

Electron transfer from copper or copper salts to alkyl halides has been used to initiate atom transfer radical additions. One modification of this process involves catalytic amounts of copper powder and fluorinated alkyl iodides the radicals so generated may react in either inter- or intramolecular fashion with alkenes (equation 13)19. Alternatively, a-chloroesters with remote alkene functions undergo cyclization in the presence of cat-... 

Evidence based on product mixtures now suggests, at least in the cases of a-halocarbonyl and perhaloalkyl starting marterials, that these reactions are in fact atom transfer radical cyclizations (equation 166)324,325. In them, the palladium catalyst is proposed to have roles both as the radical initiator and as a trap for iodine, similar to the more commonly used hexabutylditin. Intramolecular allyl halide-alkyne cyclizations proceed with trans-addition to the triple bond this is evidence that a still different mechanism may be operating in these cases (equation 167)1,326. 

The radical intermediates from Cr(II) reduction of alkyl halides can in principle be used synthetically, but have only seen limited attention to this point. co-Haloalkynes (bromides, iodides), in the presence of excess Cr(C104)2, undergo cyclization reactions to form exo-alkylidene cycloalkanes (equation 176)347. These reactions proceed by the radical cyclization of intermediate 42 onto the alkyne unit, which undergoes subsequent reduction by Cr(II) to give a hydrolytically unstable vinylchromium(III). Rings of four, five and six members can be formed. Alternatively, a-iodo esters undergo intramolecular atom transfer radical cyclizations onto alkynes or alkenes with catalytic or stoichiometric amounts of... 

These results show that not only are novel radical-anions formed by interaction of Michael acceptors with I and related organometallics, but that the epr technique is an excellent method of ascertaining the basicity of the latter, as well as shedding light on the subtle aspects of the donor-acceptor interactions involved. The chemistry in Equation (1) is exactly analogous to that which occurs in initiation of Atom Transfer Radical Polymerization (ATRP) catalysis, Equation (2), where the same basic metal complexes and others are active (X = halide). 

Although ROMP or ADMET reactions hold a prominent position among polymerisation processes initiated by NHC-Ru complexes, other catalytic paths leading to macromolecular products were also investigated. The activity of compounds 30 and other similar monometallic [(NHQRuCl2(p-cymene)] complexes was tested in the atom transfer radical polymerisation (ATRP) of vinyl monomers by Delaude and Demonceau, along with 32. These complexes led to the controlled polymerisation of methyl methacrylate at 85 °C (Equation (7.8)). Attempts to polymerise n-butyl acrylate and styrene turned out to be more challenging, because of difficulties to control the acrylate polymerisation and of competition with the self-metathesis of styrene. 

Marked contrasts in the effects of molecular structure on hydrogen-atom transfer reactions (equation 6) and the corresponding proton-transfer reactions (equation 2) have been found. The former reaction involves no change in charge (all species are univalent cations). Consequently polarization effects of hydrocarbon substituents are minimal, but large effects of delocalization of charge and spin densities in the cation radicals are observed. 

Note that under these conditions the thermal reaction in equation (90) is too slow to compete.) Finally, the stoichiometry for the oxygen-atom transfer from NO to the donor cation radical in equation (93) is independently established by the reaction of isolated cation radical intermediates with NO. 251,252... 

It is proposed that 32 reacts from its nn excited state by the nitro-to-nitrite (33) inversion followed by nitrite homolysis, when the naphthoxy radical must diffuse away from the cages to obtain the dimerization intermediate 35. However, the source of oxidizing agents is not identified. In comparison, o-nitro-ferf-butylbenzenes 37 are excited to undergo intramolecular H-atom transfer and cyclization to give indol-IV-oxides 40 (equation 34)38. The discrepancy may arise from the nature of the excited state, e.g. that of 37 may react from its njr state. 

The unimolecular reactions of CH3CH2CH2O2 were studied in detail (Fig. 6) complete potential energy surfaces were generated using both DFT [B3LYP/ 6-31+G(d,p) and mPWlK/6-31+G(d,p)] and CBS-QB3 methods. As expected, 1,5-H transfer [Equation (34)] occurs with the lowest barrier, followed by simultaneous 1,4-H transfer and HO2 expulsion [Equation (31)]. The overall decompositions of each H-atom transfer product (i.e., each QOOH radical) were modeled. It... 

By contrast, for iodide 18 having the triple bond activated by a phenyl group, conversion to the cyclic organozinc species 25 occurred effectively and the latter could be efficiently functionalized, provided that traces of moisture were excluded by pre-treatment of zinc powder with Mel. The substituted benzylidene cyclopentanes 26 and 27 were respectively obtained after iodinolysis and palladium-catalyzed cross-coupling reaction with benzoyl chloride (equation 10). However, it could not be assessed whether the formation of organozinc 25 was attributable to an anionic or a radical cyclization pathway (or both) as, had iodide 26 been produced by a radical iodine atom-transfer, it would have been converted to 25 by reaction with metallic zinc due to the presence of the activating phenyl group21. 

Addition of excess CH3I to a solution of [Ni (tmc)]+ results in the rapid loss of the absorption (A = 360 nm, e = 4 x 103 M-1 cm-1) and appearance of a less intense band at A = 346 nm. A subsequent slower reaction gives rise to the weaker absorbance profile of [Ni"(tmc)]2+. The data are interpreted in terms of the formation of an organo-nickel(II) species followed by a slower hydrolysis with breaking of the Ni-C bond. Kinetic studies under conditions of excess alkyl halide show a dependence according to the equation — d[Ni1(tmc)+]/cft = 2 [Ni(I)][RX]. The data have been interpreted in terms of a ratedetermining one-electron transfer from the nickel(I) species to RX, either by outer-sphere electron transfer or by halogen atom transfer, to yield the alkyl radical R. This reactive intermediate reacts rapidly with a second nickel(I) species ... 

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