Oxidation oxidative homocoupling

Three oxidative reactions of benzene with Pd(OAc)2 via reactive rr-aryl-Pd complexes are known. The insertion of alkenes and elimination afford arylalk-enes. The oxidative functionalization of alkenes with aromatics is treated in Section 2.8. Two other reactions, oxidative homocoupling[324,325] and the acetoxylation[326], are treated in this section. The palladation of aromatic compounds is possible only with Pd(OAc)2. No reaction takes place with PdCl2. 

The oxidative homocoupling of benzene with Pd(OAc)2, generated in situ from PdCl2 and. AcONa, affords biphenyl in 81% yield. In the absence of AcONa, no reaction took place. Pd(OAc)2 itself is a good reagent for the coupling[324-326]. The scope of the reaction has been studied[327,328]. 

Novel heteroquaterphenoquinones were synthesized by a stepwise cross-coupling reaction or by a more convenient one-pot oxidative homocoupling reaction of the heterocycle-substituted phenols (Scheme 20, <96JOC4784 see also 95TL8055>). 

For the development of the oxidative homocoupling reaction, in 1955 Chodkiewicz and Cadiot explored a Cu(I)-catalyzed heterocoupling reaction of terminal alkynes with 1-bromoalkyne in the... 

Ranu and Banerjee developed a [bmim][OH] TSIL for oxidative homocoupling of terminal alkynes to 1,4-disubstituted 1,3-diynes in atmospheric conditions using Cu(ii) without using either palladium catalyst, amines, oxidants or organic solvents. Significant advantages stated by the authors include fast kinetics, high yields and mild reaction conditions. 

Although difluoroenoxysilanes are typical nucleophiles, they can also react with other nucleophiles via their oxidation into radical cations. The oxidative homocoupling and the cross-coupling with heteroaromatics and alcohols proceeds very well in the presence of Cu triflate as the oxidizing reagent (Figure 2.24). " ... 

The di-copper-substituted y-Keggin silicotungstate [y-H2SiWio036Cu2( j,-l, 1-N3)2]4- could act as an effective homogeneous catalyst for the oxidative homocoupling of various kinds of alkynes, including aromatic, aliphatic and heteroatom-containing ones (6.8) [108] ... 

Oxidative homocoupling of aromatic and heteroaromatic rings proceeds with Pd(OAc)2 in AcOH. Biphenyl (165) is prepared by the oxidative coupling of benzene [104,105], The reaction is accelerated by the addition of perchloric acid. Biphenyl-tetracarboxylic acid (169), used for polyimide synthesis, is produced from dimethyl phthalate (168) commercially [106], Intramolecular coupling of the indole rings 170 is useful for the synthesis of staurosporine aglycone 171 [107]. 

Biaryls and 1,3-dienes can be synthesized by the Pd-promoted oxidative homocoupling of different substrates. The homocoupling of the arylstannane 172 and the alkenylstannane 175 gives the biaryl 173 and 1,3-diene 176 using a catalytic amount of Pd(OAc)2 and 02 in the presence of the iminophosphine ligand 174, or in the absence of ligand [107a]. 

Yamaguchi, S. Ohno, S. Tamao, K. Palla-dium(II)-catalyzed oxidative homocoupling of aryl—metal compounds using acrylate dibromide derivatives as effective oxidants. Synlett 1997, 1199-1201. 

A. Base-free oxidative homocoupling of arylboronic esters. Tetrahedron Lett. 2003, 44, 1541-1544. 

As already mentioned, there have been few mechanistic examinations of the copper-catalyzed Cadiot-Chodkiewicz heterocoupling reaction. Kinetic studies with the less reactive chloroalkynes [11a] have led to the assumption, shown in Scheme 7, that coupling between alkynes and haloalkynes proceeds through initial formation of copper(I) acetylides, probably formed by an acetylenic activation process similar to that described above for oxidative homocouplings. Subsequently, two reaction pathways may be reasonable ... 

Oxidative homocoupling Glaser-Hay polymerization of compound 1 [5] - ,poly[trans-bis (Z)-4-ethynyl-6-(triisopropylsilyl)-3-[(triisopropyl-silyl)ethynyl]-hex-3-ene-l,5-diynyl bis(triethylphosphane)platinum(ll)] (2)... 

Racemic synthesis of double helical octaphenylene 67 was carried out via a convergent route. In the annelation step, the Cu(II)-mediated oxidative homocoupling of dilithiotetraphenylene, derived from the dibromotetraphenylene 66, gave octaphenylene 67 (Fig. 15.25) [107]. 

Diacetylene-bridged dimers 18, 25, and 28 were more conveniently prepared (47-68% yields after Zemplen treatment) by a modified Glaser (27) oxidative homocoupling under Hay s conditions (28) of the corresponding ethynylphenyl mannosides using copper(II) acetate in refluxing pyridine (48 h.). 

A novel approach to a sexithiophene relying on metalation of the terthiophene 30 has been reported, wherein treatment of its lithio-derivative with dppfPtCL gave the complex 31, which could in turn be converted to the target molecule 32 by an oxidative homocoupling... 

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