Copper catalysts Stille coupling

The Stille coupling of 2-chloro-5-tributylstannylpyridine with an enantiopure 2-iodo-cyclohexenon (7.29.) derivative formed the basis of the total synthesis of (+)-epibatidine. The reaction is a nice example of the chemical inertness of arylstannanes and the mildness of the coupling conditions. Both the enone moiety and the chiral ally lie centre remained untouched in the process. The effective coupling required the use of a soft ligand, triphenylarsine and the addition of copper(I) iodide as co-catalyst.40... 

Cross-coupling reactions 5-alkenylboron boron compounds, 9, 208 with alkenylpalladium(II) complexes, 8, 280 5-alkylboron boron, 9, 206 in alkyne C-H activations, 10, 157 5-alkynylboron compounds, 9, 212 5-allylboron compounds, 9, 212 allystannanes, 3, 840 for aryl and alkenyl ethers via copper catalysts, 10, 650 via palladium catalysts, 10, 654 5-arylboron boron compounds, 9, 208 with bis(alkoxide)titanium alkyne complexes, 4, 276 carbonyls and imines, 11, 66 in catalytic C-F activation, 1, 737, 1, 748 for C-C bond formation Cadiot-Chodkiewicz reaction, 11, 19 Hiyama reaction, 11, 23 Kumada-Tamao-Corriu reaction, 11, 20 via Migita-Kosugi-Stille reaction, 11, 12 Negishi coupling, 11, 27 overview, 11, 1-37 via Suzuki-Miyaura reaction, 11, 2 terminal alkyne reactions, 11, 15 for C-H activation, 10, 116-117 for C-N bonds via amination, 10, 706 diborons, 9, 167... 

Farina et al. have shown that copper(I) can accelerate Stille coupling reactions [208], but examples of copper-induced cross-coupling in the absence of palladium catalysts have also been described recently. 

In 1971, Kochi reported that a catalytic silver salt induced Grignard coupling reaction with organic halides to form hydrocarbons [428,429 Eqs. (185), (186) and (187) 22,428]. However, the pair- [see Eq. (185)] and the stereoselectivity [see Eq. (187)] were not satisfactory hence, similar reactions with copper, nickel, or palladium catalysts are far more common. If a coupling reaction to be carried out involves RMgX and RX having the same R group, a silver catalyst still finds a use [Eq. (188) 430]. 

Bromo- and 4-bromoalkyl-2,5-diphenyloxazole 38 were subjected to the Stille coupling with a range of commercially available tributyltin reagents. Tri-2-furylphosphine/ Pd2(dba)3 was used as an effective catalyst. Copper(n) oxide enhanced the Stille coupling reactions of 2,5-diphenyl-4-tributylstannanyloxazole with various electrophiles [41]. Such method offered an efficient synthetic route to prepare resins from oxazole-containing monomers such as 2,5-diphenyl-4-vinyloxazole. 

Alkyne cross-coupling reactions over the last 25 years have become one of the most valuable assets in the synthetic chemist s toolbox. The now famous Sonogashira coupling (50, 114) of terminal alkynes with aryl or vinyl halides is readily achieved with a palladium catalyst, a copper(l) cocatalyst, and amine base. In the catalytic cycle (Scheme 14a), copper-and palladium-alkyne complexes are the key intermediates that lead to coupling of R and R units via the alkyne. Analogously, the Stille coupling... 

The dibromofuran 2.40 was subjected to a sequence of Stille coupling reactions, the second one requiring a more robust catalyst, leading to rosefuran 2.43 after hydrolysis and copper-catalysed thermal decarboxylation (Scheme 2.15). A quite different synthesis of rosefuran may be found in Scheme 11.48. 

The catalyst used is often palladium (0) (like Pd(PPh3)4, Pd2(dba)3), or a source of palladium (II) (like Pd(OAc)2, BnPdCl(PPh3)2 to name a few that gets reduced to the active species palladium(O) in situ. Methods using other metals like manganese, copper, and nickel have been reported the latter has been applied for instance in the successful Stille coupling of unreactive aryl chlorides as well as in the coupling of unactivated primary and secondary alkyl halides. ... 

It is reported in literature that additives like LiCl or Cu(I) salts can have a dramatic influence on the coupling. The copper effect in Stille coupling reactions was investigated by Farina and Liebeskind and coworkers. For instance in the reaction of iodobenzene and vinyltributyltin in dioxane at 50 °C catalyzed by Pd2(dba)3 in presence of a strong ligand like PPhs, it was found that the addition of 2 molar equivalents of Cul per mol of catalyst led to a > 100 fold increase in reaction rate. 

The following examples illustrate the scope of the Stille coupling. For example, triphenylarsine and/or copper co-catalysts are beneficial for the performance of stannanes. Triflates can be coupled in the presence of bromides. 

In a recent review it was argued that such additives of copper, benzoquinone, and HPMOV are not really needed all that is needed is the presence of oxidation-resistant ligands that prevent palladium metal formation [15]. Indeed, activation of the C-H bond is not as slow as, for example, the Wacker reaction of ethene in which reoxidation of palladium must be performed by copper oxidation, although in this catalytic system the additives may still play a role in stabilizing the intermediate low-valent palladium species and thus prevent catalyst decomposition. This thesis was corroborated by the work of de Vos and Jacobs, who showed that addition of benzoic acid to the oxidative arylation reaction in the presence of oxygen led to superior results in the coupling of a variety of substituted arenes with acrylates, cinnamates, and ,/f-unsaturated ketones. Very good yields and TON up to 762 were obtained at 90 °C. A mixture of the o, m, and p isomers is obtained if substituted arenes are used [16]. 

The coupling of terminal alkynes with aryl or vinyl halides under palladium catalysis is known as the Sonogashira reaction. This catalytic process requires the use of a palladium(0) complex, is performed in the presence of base, and generally uses copper iodide as a co-catalyst. One partner, the aryl or vinyl halide, is the same as in the Stille and Suzuki couplings but the other has hydrogen instead of tin or boron as the metal to be exchanged for palladium. 

This review is divided into four main sections, covering the Heck, Stille, and Suzuki reactions, with miscellaneous reactions being included at the end. Processes featuring alkynes in copper co-catalyzed Sonogashira-type couplings have been included in the section on Heck reactions. This review does not cover carbon-carbon bond formation processes using immobilized catalysts. Similarly, fluorous-phase syntheses " and those on polyethylene glycol " are excluded. 

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