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Hypervalent iodine complex

More involved studies of the oxidation of plant phenols [27], as well as the introduction of thallium and hypervalent iodine complexes and the use of electrochemical methods, have emphasized the importance of another intermediate involved in oxidative coupling reactions, namely the phenoxonium ion 8 [28-30]. Due to its ionic nature, reaction through an oxo-nium ion can improve the regioselectivity of bond formation and lead to fewer unwanted products (for example, no coupling via the oxygen atom). The coupling reaction can then be viewed as an electrophilic aromatic substitution between 17 and a nucleophilic aromatic unit 15 (Scheme 5). [Pg.482]

Hypervalent Iodine Chemistry. The formation of hypervalent iodine complexes is often promoted by TMSOTf. Thus, TMS-alk)mes can be transformed with iodosobenzene and TMSOTf into phenyl iodonium triflates in moderate to good yields, which may be subsequently converted into alkyneamides (eq 102). ... [Pg.531]

Scheme 5.37 Arduengo s synthesis of the first hypervalent iodine complex featuring an NHC (254). Scheme 5.37 Arduengo s synthesis of the first hypervalent iodine complex featuring an NHC (254).
In 1991, Arduengo isolated one of the first NHC-Group 17 element adducts. The team found that NHCs cleanly reacted with iodopentafluoro-benzene to form hypervalent iodine complex 254 (Scheme 5.37). According to the NMR data, complex 254 was fluxional in solution, and in equilibrium with the free carbene and iodopentafluorobenzene. After several hours at room temperature, solutions of 254 were shown to undergo cleavage of the I-Cph bond, generating pentafluorobenzene and the 2-iodoimidazolium ion 255. [Pg.252]

Common alcohol oxidation methods employ stoichiometric amounts of toxic and reactive oxidants like Cr03, hypervalent iodine reagents (Dess-Martin) and peracids that pose severe safety and environmental hazards in large-scale industrial reactions. Therefore, a variety of catalytic methods for the oxidation of alcohols to aldehydes, ketones or carboxylic acids have been developed employing hydrogen peroxide or alkyl hydroperoxides as stoichiometric oxygen sources in the presence of catalytic amounts of a metal catalyst. The commonly used catalysts for alcohol oxidation are different MoAV(VI), Mn(II), Cr(VI), Re(Vn), Fe(II) and Ru complexes . A selection of published known alcohol oxidations with different catalysts will be presented here. [Pg.492]

Similar hypervalent iodine radicals (9-1-2) are formed in the reaction of alkyl radicals with alkyliodides (R + RI — R2I ), and as an intramolecular complex they are stable enough that a reaction with 02 is only low (Miranda et al. 2000). Such 9-X-2 radicals have also been postulated as intermediates in the reduction of alkylhalides by a-hydroxyalkyl radicals (Lemmes and von Sonntag 1982). [Pg.89]

The Dess-Martin periodinane 30 (1,1,1 -triacetoxy-1,1 -dihydro-1,2-benziodoxol-3(7H)-one) was originally described in 1983 and has become a widespread reagent for the oxidation of complex, sensitive and multifunctional alcohols.15 The periodinane is a hypervalent iodine species and a number of related compounds also serve as oxidizing agents. [Pg.14]

Vinyliodonium ions, 35 and 36, are hypervalent iodine species in which one or two alkenyl ligands are bound to a positively charged iodine(III) atom. Although they are reactive with nucleophilic reagents, they are less labile than alkynyliodonium ions, and stable halide salts of vinyliodonium ions can be prepared. The first vinyliodonium compounds [i.e. (a, / -dichlorovinyl)iodonium salts] were synthesized by the treatment of silver acetylide-silver chloride complexes with (dichloroiodo)arenes or l-(dichloroiodo)-2-chloroethene in the presence of water (equation 152). The early work was summarized by Willgerodt in 1914115. This is, of course, a limited and rather impractical synthetic method, and some time elapsed before the chemistry of vinyliodonium salts was developed. Contemporary synthetic approaches to vinyliodonium compounds include the treatment of (1) vinylsilanes and vinylstannanes with 23-iodanes, (2) terminal alkynes with x3-iodanes, (3) alkynyliodonium salts with nucleophilic reagents and (4) alkynyliodonium salts with dienes. [Pg.1229]

The question as to whether the reactive intermediate is the phenol-metal/leaving group complex 21/22 or the free phenoxonium ion 17 has been studied in the particular case of hypervalent iodine. Pelter and co-workers presented permissive evidence in support of a mechanism involving the free oxonium species 17 (Scheme 7) Phl(OAc) is an extremely good nucleofuge, no transfer of chirality is observed when homochiral hypervalent iodine compounds are used, and calculations made on the cation species correctly predict the re-gioselectivity of the substitution reaction [32, 33]. [Pg.483]

Tohma, H., Kita, Y. Hypervalent iodine reagents for the oxidation of alcohols and their application to complex molecule synthesis. Adv, Syn, Catal. 2004, 346, 111-124. [Pg.574]

The new methods (Schemes 23-25) valuable for the synthesis of complex pyrroloiminoquinone alkaloids are based on the hypervalent iodine-induced nucleophilic substitution of p-substituted phenol ethers via reactive cation radical intermediates. Thus, we found a novel hypervalent iodine induced nucleophilic substitution of p-substituted phenol ethers in the presence of a variety of nucleophiles, such as TMSN3, TMSOAc, and (3-diketones, etc., in 1994. For this reaction the reaction solvent was quite important, and CF3CH2OH and (CF3)2CHOH worked very well (Scheme 23) [76]. [Pg.150]

Primary amines RNH2 (R = i-Pr, /-Bu, t-Bu or cyclohexyl) react with the carbamate Et02CN=CCl2 to yield the carbodiimides Et02CN=C=NR. A new method of preparing imines is to add a carbonyl compound (2,6-dimethylcyclohexanone, 2-tetralone, 2-decalone etc.) to a preformed complex of a primary amine (t-butylamine, cyclohexylamine, benzylamine or 1-phenylethylamine) and titanimn(IV) chloride suspended in hexane or octane. Primary amines R NH2 (R = t-Bu, N=C, Tos or phthalimido) react with nitroso compounds R NO (R = r-Bu, pyrrolidin-l-yl, Ph or 2-MeCC6H4) in the presence of the hypervalent iodine compound Phi (OAc)2 to give... [Pg.583]

The L -iodane PhI(OAc)2 has been used extensively, most notably by Sanford, to oxygenate the C-H bonds of arenes and even alkanes in the presence of palladium catalysts." Interestingly, this reaction was likely mediated by a binuclear complex featuring two Pd(III) atoms joined by a palladium-palladium (Pd-Pd) bond however, this complex can disproportionate into a Pd(IV)-Pd(II) complex without a formal Pd-Pd bond, and this intricate interplay is often controlled by the presence and nature of hypervalent iodine oxidants." We discovered that this reaction manifold could be extended to include the amination of arene substrates heating 2-phenylindole 51 in the presence of the -iodane 49 and palladium acetate provided the ortho-aminated product 52 in a 19% yield however, switching the metal from palladium acetate... [Pg.166]


See other pages where Hypervalent iodine complex is mentioned: [Pg.1756]    [Pg.11]    [Pg.531]    [Pg.251]    [Pg.1756]    [Pg.11]    [Pg.531]    [Pg.251]    [Pg.27]    [Pg.172]    [Pg.620]    [Pg.583]    [Pg.131]    [Pg.214]    [Pg.2]    [Pg.5]    [Pg.26]    [Pg.482]    [Pg.483]    [Pg.124]    [Pg.420]    [Pg.53]    [Pg.703]    [Pg.136]    [Pg.141]    [Pg.208]    [Pg.478]    [Pg.379]    [Pg.387]    [Pg.309]    [Pg.23]    [Pg.120]    [Pg.172]    [Pg.40]    [Pg.366]    [Pg.281]    [Pg.1000]    [Pg.27]    [Pg.354]   
See also in sourсe #XX -- [ Pg.225 ]




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