Radical reductive aryl

Other limitations of the reaction are related to the regioselectivity of the aryl radical addition to double bond, which is mainly determined by steric and radical delocalization effects. Thus, methyl vinyl ketone gives the best results, and lower yields are observed when bulky substituents are present in the e-position of the alkene. However, the method represents complete positional selectivity because only the g-adduct radicals give reductive arylation products whereas the a-adduct radicals add to diazonium salts, because of the different nucleophilic character of the alkyl radical adduct. ... 

RADICAL ANION ARYLATION, 58, 134 Raney nickle, 57, 19, 58, 114, 116 Raney nickel,W-2, 56, 16, 74 Reduction, carboxyl groups, 56,83 Reductive alkylation, 56, 52 Resolution of amines, 55, 80, 83 Rexyn 201, 55,4 Rhodium(III) oxide, 57,1 Ring contraction, 56. 107... 

Reductive arylation of enones, TiCl3 induces homolytic dediazotization of diazonium salts to produce aryl radicals, which arylate electron-deficient alkenes.1 Example ... 

Radical reductive alkylation of enamines has also been utilized for the intramolecular cyclization reaction34. Enamine 38 bearing an exo-olefin moiety, on treatment with Bu3SnH in the presence of a radical initiator, generates an aryl radical 39 which undergoes exclusive 1,6-cyclization to give the isoquinoline 40 as the sole product in 51.3% yield (equation 9). 

The mechanism is by no means completely clear, but the photodehalogenation reaction is postulated to occur through the formation of a pair of radical ions from an exciplex resulting in the excited state (Grimshaw and de Silva, 1981). The precursor of the reduction product (Aryl-H) is suggested to be a radical anion (Aryl-Ck-), while a radical cation (Aryl-Cl+ ) is postulated as the precursor of the substitution product (Aryl-OR). In a less polar solvent, e.g., iso-propanol, direct homolysis of the C-Cl bond occurring from the triplet state has been suggested,... 

Enone reduction. 2,6-Di-t-butyl-p-quinols give the 4-hydroxycyclohexenones. Formation of aryl radicals. Reduction of aryl bromides proceeds via radical intermediates. Addition to a side-chain double bond in such reactions is observed. 

Raman, IR, and near-IR spectroscopy and TGA analyses of the functionalized SWNTs confirmed the attachment of radical groups. Aryl diazonium salts have been used to generate radicals for addition to SWNTs using electrochemical reduction.Up to 49wt% aryl functionality has been achieved and a stable homogeneous solution of aryl functionalized SWNT (50 mg L ) up to 36 h in chloroform is obtained after a 30 min sonication. Polymeric radical addition to SWNTs has been shown to occur during in situ free radical polymerization of styrene in toluene and sodium 4-styrenesulfonate in water. 

On reduction of aryl halides, the initially formed radical anion decomposes to halide ion and the aryl radical the aryl radical is generally more easily reduced than the substrate or it may abstract a hydrogen atom from the solvent system, but in suitably substituted compounds the radical may attack a phenyl ring with ring closiue. Thus, for example, 5-(2-chlorophenyl)-l-phenylpyrazole is reduced to pyra-zolo[l,5-/]phen-anthridine. 

The mechanism of S , l reaction was established on the basis of direct electrochemical methods. Indeed the nucleophilic attack in eqn.15 competes with the a-aryl radical reduction in eqn.8. When the former constitutes the main route for Ar evolution, the apparent electron number involved in the halide wave tends to zero (when ArNu— reoxidizes) or to one (when ArNu is stable) electron. This enables then... 

Beyer synthesis, 2, 474 electrolytic oxidation, 2, 325 7r-electron density calculations, 2, 316 1-electron reduction, 2, 282, 283 electrophilic halogenation, 2, 49 electrophilic substitution, 2, 49 Emmert reaction, 2, 276 food preservative, 1,411 free radical acylation, 2, 298 free radical alkylation, 2, 45, 295 free radical amidation, 2, 299 free radical arylation, 2, 295 Friedel-Crafts reactions, 2, 208 Friedlander synthesis, 2, 70, 443 fluorination, 2, 199 halogenation, 2, 40 hydrogenation, 2, 45, 284-285, 327 hydrogen-deuterium exchange, 2, 196, 286 hydroxylation, 2, 325 iodination, 2, 202, 320 ionization constants, 2, 172 IR spectra, 2, 18 lithiation, 2, 267... 

This synthesis is only one example of a wide range of reactions which involve aryl (or alkyl) radical addition to electron-deficient double bonds resulting in reduction.The corresponding oxidative reaction using aryl radicals is the well known Meerwein reaction, which uses copper(II) salts. 

An alternative reaction mechanism has been suggested for nitroarylation of enolates. An impetus for considering other mechanisms is the fact that the by-products which might be expected from aryl radicals, such as reduction products from hydrogen abstraction from the solvent or biaryls from coupling, are not observed. One alternative is that, rather than being a chain process, the reaction may involve recombination whereby the radicals combine more rapidly than they separate. 

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