Halide-olefin coupling reactions

Palladium-catalyzed coupling reactions of organic halides with olefins or dienes (R. F. Heck, 1979) are broad in scope and simple to carry out. Anhydrous conditions or any special technique are not required and most functional groups are tolerated. 

Cross-coupling reactions of aromatic or vinylic halides and olefins catalyzed by palladium. 

Ternary Pd-catalyzed coupling reactions of bicyclic olefins (most often norbor-nadiene is used) with aryl and vinyl halides and various nucleophiles have been investigated intensively over the past few years [44]. A new approach in this field is to combine Heck and Suzuki reactions using a mixture of phenyliodide, phenyl-boronic acid and the norbornadiene dicarboxylate. Optimizing the conditions led to 84% of the desired biphenylnorbornene dicarboxylate [45]. Substituted phenyl-iodides and phenylboronic acids can also be used, though the variation at the norbornadiene moiety is highly limited. 

As shown in the previous sections, a (cr-allenyl)palladium species, which is formed from a propargyl electrophile and a Pd(0) catalyst, reacts with a hard carbon nucleophile in a manner analogous to the Pd-catalyzed cross-coupling reaction to give a substituted allene. The results indicate that the reactivity of the (cj-allenyl)palladium species is similar to that of an alkenylpalladium intermediate. Indeed, it was found that the (cr-allenyl)palladium species reacted with olefins to give vinylallenes, a reaction process that is similar to that of the Heck reaction of alkenyl halides [54]. 

This article presents the principles known so far for the synthesis of metal complexes containing stable carbenes, including the preparation of the relevant carbene precursors. The use of some of these compounds in transition-metal-catalyzed reactions is discussed mainly for ruthenium-catalyzed olefin metathesis and palladium-Znickel-catalyzed coupling reactions of aryl halides, but other reactions will be touched upon as well. Chapters about the properties of metal- carbene complexes, their applications in materials science and medicinal chemistry, and their role in bioinorganic chemistry round the survey off. The focus of this review is on ZV-heterocyclic carbenes, in the following abbreviated as NHC and NHCs, respectively. 

C. Chen, K. Wilcoxen, C.Q. Fluang, N. Strack, J.R. McCarthy, New methods for the synthesis of fluoro olefins via the palladium catalyzed cross-coupling reaction of 1-fluorovinyl halides with organoboranes and organostannanes, J. Fluor. Chem. 101 (2000) 285-290. 

The alkenylmagnesium species generated by the Fe-catalyzed arylmagnesiation can be trapped by electrophiles. For example, the cross-coupling reaction of the alkenyhnagne-sium species with an aryl halide is achieved with a nickel catalyst, giving a tetrasubstituted olefin 21 in good overall yield (Scheme 17). ... 

The first step in the cycle, analogous to the cross-coupling reactions, is the oxidative addition of an aryl (vinyl) halide or sulfonate onto the low oxidation state metal, usually palladium(O). The second step is the coordination of the olefin followed by its insertion into the palladium-carbon bond (carbopalladation). In most cases palladium is preferentially attached to the sterically less hindered end of the carbon-carbon double bond. The product is released from the palladium in a / -hydrogen elimination and the active form of the catalyst is regenerated by the loss of HX in a reductive elimination step. To facilitate the process an equivalent amount of base is usually added to the reaction mixture. 

Catalytic formation of carbon-carbon bonds is a powerful tool for construction of complex molecular architectures, and has been developed extensively for applications in organic synthesis. Three main classes of carbon-carbon bond forming reactions have been studied in sc C02 carbonylation (with particular attention paid to the hydroformylation of a-olefins), palladium-catalyzed coupling reactions involving aromatic halides, and olefin metathesis. 

The subsequent. mi-elimination, yielding a 1,2-substituted alkene and hydrido-palladium halide, is, however, reversible, and therefore the thermodynamically more stable (E )-alkene, ( )-RCH=CHZ, is generally produced when the coupling reaction is performed with a terminal olefin. It is worth mentioning that the formation of this 1,2-disubstituted alkene is accompanied with the formation of 1,1-disubstituted alkene, CH2 = C(Z)R, the amount of which depends on the kind of catalyst and the reaction conditions, a lower reaction... 

Lipshutz and colleagues presented recently palladium-catalyzed direct coupling reactions of alkyl iodides and vinyl bromides or iodides catalyzed by 1 mol% Pd(amphos)Cl2 in the presence of zinc and TMEDA in a biphasic aqueous/poly-(ethylene glycol tocopheryl sebacate) reaction medium [198], Internal olefins were obtained in 51-95% yield. For aryl-substituted (Aj-vinyl bromides, retention of double bond geometry was observed, while different degrees of isomerization occurred for (Z)-isomers, which may indicate the intervention of a radical addition process in the course of the coupling process. Alkyl-substituted (Z)-vinyl halides were transformed in contrast with retention of alkene geometry. Aryl halides also reacted [199],... 

Preparation of symmetrical and unsymmetfical aliphatic ethers can be accomplished by coupling alkyl halides and sodium alkoxides (H illiamson). The formation of the alkoxide may be slow and incomplete because the slow-dissolving alkoxide coats the sodium. This difficulty can be overcome by using a large excess of alcohol. After the sodium has dissolved, the alkyl halide is added to form the ether which is finally removed by fractional distillation. Sodium f-butoxide is not only formed slowly but also reacts very slowly with alkyl halides. The reaction of the f-alkyl halide with the sodium alcoholate is not any better, for the chief products are olefins. Consequently, another method must be considered for preparing f-alkyl ethers (method 118). Even in the conversion of s-alkyl halides, olefin formation occurs. 

Even though there is an instance in which stereochemistry of the olefinic halide was not retained in the product [Eqs. (143) and (144) 296, but see also Ref 260], a number of coupling reactions [see Eqs. (123), (128), (129), (132), (134), (135), (139), (146), and (149)] verified that the process took place with virtually complete retention of configuration of olefinic substrates which, no doubt, is an outstanding feature of this method. 

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