Homocoupling reactions

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... 

These nickel- or palladium-catalyzed homocoupling reactions can also be conducted in the presence of zinc as reducing agent, leading usually to comparable results as shown recently in the palladium-catalyzed dimerisation of aryltrif-lates [30]. 

It was shown a few years ago that a-haloesters can react with an aryl-nickel compound generated electrochemically in a divided cell (Eq. 8) [57]. The main drawback for this two-step method is the use of a large excess of PPhs to prevent the homocoupling reaction ... 

Non-steroidal anti-inflammatory a-arylpropionic acids were also prepared from the corresponding benzylic chlorides and CO2 using as catalyst Ni-dppe or Ni-dppp in the presence of COD (Table 16) [103]. The use of the catalyst in this reaction is not absolutely required but its use limits the homocoupling reaction which would be the main process at high concentration of the benzylic halide and low pressure of CO2 [104]. 

Cross-over experiments suggest that the homocoupling reaction occurs between an alkenyl telluride and an alkenyl Pd species, which is formed via the migration of an alkenyl moiety from Te to Pd. 

The first iron-mediated homocoupling reaction was described in 1939 by Gilman and Lichtenwalter. They showed that phenyhnagnesium iodide reacts with a sub-stoichio-metric amount of iron(II) chloride, in diethyl ether, to give biphenyl in 98% yield (Scheme 45). 

The addition of substituted allylic zinc reagents to aldehydes is usually unselective" . Furthermore, the direct zinc insertion to substituted allylic halides is complicated by radical homocoupling reactions. Both of these problems are solved by the fragmentation of homoallylic alcohols. Thus, the ketone 166 reacts with BuLi providing a lithium alcoholate which, after the addition of ZnCl2 and an aldehyde, provides the expected addition product... 

These a-functionalized lithiosilanes are stable for up to 6 days at 0°C, when at least one substituent at silicon is an aryl group. Alkylated mono- or diaminochlorosilanes, however, undergo with lithium in THF homocoupling reactions to yield the corresponding symmetrical di- and tetraaminodisilanes (equation 40)89. 

Reduction of diaryl thioketones with ytterbium metal affords a mixture of the corresponding thiols and diarylmethanes together with products arising from homocoupling reactions (equation 119)433. 

He, H.S., Zhang, C., Ng, C.K.-W. and Toy, P.H. (2005a) Polystyrene-supported triphenylarsines useful ligands in palladium-catalyzed aryl halide homocoupling reactions and a catalyst for alkene epoxidation using hydrogen peroxide. Tetrahedron, 61(51), 12053-57. 

Kuroboshi, M. Waki, Y. Tanaka, H. Palladium-catalyzed tetrakis(dimethylamino)ethy-lene-promoted reductive coupling of aryl halides./. Org. Chem. 2003, 68, 3938-3942. Luo, F.-T. Jeevanandam, A. Basu, M. K. Efficient and high-turnover homocoupling reaction of aryl iodides by the use of palladacycle catalysts. A convenient way to prepare poly-p-phenylene. Tetrahedron Lett. 1998, 39, 7939-7942. 

Ogoshi, S. Nishiguchi, S. Tsutsumi, K. Kurosawa, H. Palladium-catalyzed reductive homocoupling reaction of 3-silylpropargyl carbon-... 

Lei, A. Zhang, X. A novel Pd-catalyzed homocoupling reaction initiated by transmetalation of Pd enolates. Tetrahedron Lett. 2002, 43, 2525-2528. 

Scheme 1. General description of (a) the oxidative Glaser-type homocoupling reaction and (b) nonoxidative Cadiot-Chodkiewicz heterocoupling (X= Br, I).

In a comparison of Cu- versus Pd-homocoupling reactions, Haley and coworkers demonstrated a connection between the selectivity of the ring forming event, the... 

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