Arenes copper catalysts

Activated aromatic compounds add to A-carbamoyl imines in the presence of copper catalysts, and with good enantioselectivity when a chiral catalyst is used. A combination of AuCls/AgOTf facilitates the addition of arenes to A-tosyl... 

Shen et aL report the use of lithium halides under copper-catalyzed aerobic conditions to effect aromatic C—H bond activation resulting in bromo- and chloro-arenes. The catalyst employed Cu(N03>2 SHjO is cheap and readily available and, importantly, the reaction is compatible with both electron-donating and electron-withdrawing substituents on the aryl rings examples are shown with the optimized reaction conditions, using LiCl as the halogen source. LiBr and NaCl also resulted in halogenation albeit in modest yields (Scheme 7.31). 

The copper-catalyzed coupling of glycolic acids with aryl iodides has been accomplished using common copper catalysts (Scheme 2.54) [79], This was a chemoselective transformation that resulted in the preferential formation of the alkyl aryl ether instead of the ester. The carboxylic acid was retained in the product and was able to be further transformed in subsequent reactions. The electronic composition of the aryl iodide did not significantly influence the outcome of the reaction, and a range of electron-rich and electron-poor arenes were well tolerated by the chemistry. 

To avoid die difliculties in bandling die bigbly air-sensitive copper arenediiolates, a metliod for dieir preparation and utilization in situ bas been developed, die aren-ediiol 29 being deprotonated witii n-BuLi and mixed widi a coppetfl) salt to yield die active catalyst [34]. 

The well-defined copper complexes 94 and 95 (Fig. 2.16) have been used as catalysts for the intermolecular hydroamination of electron-deficient alkenes [Michael acceptors, X=CN, C(=0)Me, C(=0)(0Me)] and vinyl arenes substituted... 

To avoid the difficulties in handling the highly air-sensitive copper arenethiolates, a method for their preparation and utilization in situ has been developed, the aren-ethiol 29 being deprotonated with n-BuLi and mixed with a copper(l) salt to yield the active catalyst [34]. 

On the other hand, Tilley et al. have reported a synthesis of a well-defined tris(tert-butoxy)siloxy-iron(lll) complex [13] as well as respective molecular siloxide complexes of cobalt [14] and copper [15], which appear to become precursors for their grafting onto silica and application as catalysts for oxidation of alkanes, alkenes and arenes by hydrogen peroxide. 

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]. 

In connection with nickel-catalysed reductive coupling reactions of dihaloarenes, leading to poly(arylene)s, the copper-catalysed reductive carbenoid coupling reactions involving substituted bis(dichloromethyl)arenes and metals or other reductants should be mentioned. The reductive carbenoid coupling of bis(phenyldichloromethyl)arene with zinc in the presence of Cu-based catalysts is shown below ... 

The first practicable synthesis of aromatic pentafluorosulfuranyl derivatives was introduced by W. A. Sheppard ]50] in 1960 ]43a]. It was based on the stepwise oxidative fluorination of diaryldisulfides with AgF2, via the trifluorosulfanyl arenes [51], to the corresponding pentafluorosulfuranyl compounds ]43b]. This early synthesis suffered from relatively low yields and sometimes bad reproducibility. Then J. S. Thrasher and coworkers ]45b-d, 481 found that the autoclave material used by Sheppard, copper, acts as a catalyst in the conversion. Copper and some other metals are supposed to facilitate the fluorination reaction via formation of metal thiolate intermediates. 

Copper is underutilized as a catalyst for C-H bond functionalization even though it was the first transition metal shown to promote carbon-hydrogen bond arylation. In 1941, Steinkopf, Leitsmann, and Hofmann showed that Ullmann reaction of 2-iodothiophene produces substantial amounts of tritiophene [88], This reaction necessarily involves one C-H bond arylation step. Subsequently, it has been shown that electron-deficient arenes such as polynitrobenzenes and pentafluorobenzene,... 

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