Alkenes Heck coupling

The coupling reaction of aryl-alkenyl halides with alkenes in the presence of a palladium catalyst and a base is known as the Heck coupling (Scheme 9.4).6 Since the early 1980s, this type of coupling reaction has been used for die syndiesis of poly(arylenevinylene) and related polymers by polymerization of AB- or AA/BB-type of monomers (Scheme 9.5).7... 

Water-soluble phosphine ligands containing m-guanidinium moieties were synthesized and applied to aqueous Heck coupling reactions.149 High temperature appears beneficial for Heck-type coupling of simple alkenes in water.150... 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

Scheme 6.6 Oxidative Heck coupling of boronic acids and alkenes using copper(ll) acetate as a reoxidant.

Reaction of organic halides with alkenes catalyzed by palladium compounds (Heck-type reaction) is known to be a useful method for carbon-carbon bond formation at unsubstituted vinyl positions. The first report on the application of microwave methodology to this type of reaction was published by Hallberg et al. in 1996 [86], Recently, the palladium catalyzed Heck coupling reaction induced by microwave irradiation was reported under solventless liquid-liquid phase-transfer catalytic conditions in the presence of potassium carbonate and a small amount of [Pd(PPh3)2Cl2]-TBAB as a catalyst [87]. The arylation of alkenes with aryl iodides proceeded smoothly to afford exclusively trans product in high yields (86-93%) (Eq. 61). 

Alkenyl trifluoromethanesulphonates (enol triflates) undergo Heck coupling with alkenes efficiently (equation 123)209a 215. This reaction is a useful variation of the use of vinyl halides not only because they are easy to prepare from the corresponding carbonyl compounds, but also because yields are good, and the stereochemistry of the triflate is largely maintained. 

Preliminary results from a study of catalytic activation of the heterocoupling between arylhalides and alkenes using pony-tail-functionalized dendrimer-encapsulated Pd nanoparticles have shown promise. For example, the classic Pd-catalyzed Heck coupling between arylhalides and methacrylate yields predominately (> 97%) the trans-cinnimaldehyde product [176]. On the other hand, the C02-soluble dendrimer nanocomposite exclusively catalyzes the production of the highly unfavored 2-phenyl-acrylic acid methyl ester isomer at 5000 psi and 75 °C (Fig. 27] [177]. 

Multiple Heck Couplings of Oligohaloarenes with Alkenes 312... 

Twofold Heck Couplings on the Same Alkene 11.09.4.1 Ethylene... 

Heck coupling of phenyl iodide with alkenes Pd(OCOCH3)2/ P(C6H5)3 B[(CH3CH2C6F13)n (n = 1,2) Solvent replacement Carroll and Holmes (1998)... 

These examples demonstrate that a selective Heck-Diels-Alder sequence with two different alkenes is only possible either in a stepwise manner, if an alkene reacts much faster in the Heck reaction than in the subsequent cycloaddition so that the 1,3-diene can be isolated, or as a real cascade reaction if one alkene is more reactive and thus selectively reacts as a coupling partner, whereas the other one is a better dienophile. Both concepts have been used by Kollar et al. for the annelation of cyclohexene rings onto the steroidal skeleton 26 (Scheme 4) [28-30]. At 60 °C the cycloaddition was sufficiently suppressed so that the Heck coupling product 29 could be isolated and subsequently subjected to Diels-Alder reactions with different dienophiles. For a domino reaction with both methyl acrylate and dimethyl fumarate (28) present in the reaction mixture, the conditions had to be precisely adjusted so that the mixed products 31 and 32 were formed predominantly along with only small amounts of the products of a twofold reaction of either 27 (R = CC Me) or 28 with 26. These conditions also proved suitable for a cascade reaction of 26 involving allyl alcohol 27 (R = CH2OH) or allyl acetate 27 (R = CH2OAc) and dimethyl fumarate (28). 

Drawn from these examples it is apparent that controlling the chemose-lectivity in inter-intermolecular Heck-Diels-Alder reactions of two different alkenes can be tedious if the alkenes show comparable reactivities. Nevertheless, the stepwise approach was realized in several other cases. In a synthesis of a derivative of cephalostatin 1 containing a central benzene instead of the pyrazine ring, Winterfeldt et al. linked two steroidal systems by a Heck coupling and subsequently performed high pressure Diels-Alder reactions of the conjugated diene with electron-deficient alkynes [34], Another example, reported by Hayashi et al., involves a selective Heck reaction of a bromoglu-cal with ethylene or acrylic acid derivatives followed by cycloadditions with maleic anhydride or N-phenylmaleimide [35]. 

The preparation of unsymmetrically terminally disubstituted 1,3,5-hexa-trienes by twofold Heck coupling of 162-m with two different alkenes cannot be achieved, since the second coupling step turned out to be significantly faster than the first one [96]. Sufficient differentiation could not be brought about with a triflate and a bromide leaving group as in 168. How-... 

Heck s reaction can result in regioisomers, depending on whether the reaction proceeds at the a or (3 carbons in the alkene. A selectivity > 99% to the a-arylation product was achieved in the Heck coupling of 1-bromonaphthalene to butyl vinyl ether in [bmim][BF4], In contrast, the same reaction in toluene, acetonitrile, DMF, or DMSO... 

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