Homocoupling reactions alkene coupling

Three oxidative reactions of benzene with Pd(OAc)2 via reactive phenylpalla-dium acetate (397) are known. The insertion of alkenes and /3-H elimination afford arylalkenes 398. This topic is treated in Section 2.2.8. Two other reactions, oxidative homocoupling [157,158] and acetoxyladon [159] 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 affords biphenyl (399). The scope of the homocoupling reaction has been studied [160,161]. The reaction was applied to commercial production of biphenyltetracarboxylate (400) by coupling of dimethyl phthalate using Pd(OAc)2 and Cu(OAc)2. Addition of phenanthroline is important for the regioselective formation of the most important 3,4,3 4 -isomer [162]. 

Intermolecular coupling of a vinyl ether with styrene at a carbon anode in methanol is successful, giving a mixture of the cross coupled product and the two homocoupled products [49], Intramolecular coupling between an enol ether and an alkene centre, as in 24 and 25, proceeds to give the cyclized product in good yield [50], Five and six membered rings can be constructed in this way. An easily oxidised vinyl ether group is necessary to initiate the reaction and the second alkene... 

The transalkylidenation of two terminal alkenes under release of ethene, catalyzed by ruthenium carbenoids (Grubbs Catalyst). Statistically, the reaction can lead to three possible pairs of geometric isomers, i.e. EJZ pairs for two homocouplings and the cross-coupling (R-CH=CH-R, R -CH=CH-R and R-CH=CH-R ) - a total of 6 products. 

The main advantage of this reaction over the McMurry reaction (see section on McMurry alkenation ) is the notion that the reaction can take place with two different ketones. In this regard the diazo-thioketone coupling is a cross-coupling rather than a homocoupling. 

Coupling reactions. Organolithium and Grignard reagents undergo homocoupling by VO(OEt)Cl2 at -78°. Alkenylboranes are converted to alkenes via migration of a S-substituent to the sp carbon, and the process is ( )-selective in the presence of a fluoride... 

A very important series of reactions are those in which two hydrocarbons such as arenes and alkenes are homocoupled with loss of two hydrogens in the presence of a stoichiometric amount of palladium(II) compounds such as PdCl2 and Pd(OAc)2, or more usefully with a catalytic amount of palladium catalysts and a stoichiometric amount of oxidantsJ f The palladium(II)-promoted coupling reaction was first reported by Hiittel and Bechter in 1959, who found that a-substituted styrenes were coupled by PdCl2 in acetic acid in the presence of NaOAc (Scheme... 

To date, most research on NHCP transition-metal catalysis has been devoted to cross-couplings [13] or related reactions such as hydroarylation of alkenes [18], direct arylation of alkynes [17], or oxidative homocoupling of terminal alkynes [19]. All NHCP systems used in these studies feature one or two... 

The chemoselectivity provided by the solid support in the cross-metathesis reaction is evident in ene-ene metathesis reactions, as both olefins are capable of a homodimerization reaction. The Mata laboratory has devoted significant effort toward the understanding and development of cross-metathesis reactions on a solid support. To probe the limits of the reaction, aliphatic, aryl, and acryloyl alkenes 8,11, and 12 were immobilized and reacted with a variety of soluble olefins 13-16 from different classifications based on homodimerization potential (Scheme 6.2). For example, the immobilized acrylate 8 was reacted with several soluble olefins to form the immobilized coupling product 9. Subsequent cleavage with TFA and esterification with diazomethane delivered the esters 10. Other immobilized alkenes explored in the same process were 11 and 12. Among other olefins, they were reacted with the soluble alkenes 13-16. Modest to good yields (shown in parentheses) were obtained, but, most importantly, no dimerization of the immobilized alkenes 8,11, and 12 was observed, and undesired homocoupling products of the alkenes 13-16 in solution were easily washed away in the workup step. 

The ability of aryl and alkenyl boronic acids to oxidatively add to Pd(0) was demonstrated by their participation in cross-coupling reactions with alkenes (752). Homocoupled products derived from organoboronic acids have been identified in Suzuki reactions. This reaction was applied to the synthesis of coupled products derived from the homocoupling of organoboroxines (755). 

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