Cross aryl tosylates

Several metal cross-coupling reactions have been applied to pyrazoles. C-H Arylation of aryl tosylates or chlorides could be achieved with a ruthenium catalyst at the C-2 phenyl position of... 

The use of aryl tosylates as electrophiles is attractive, since they can be synthesized from readily available phenols with less expensive reagents than those required for the preparation of the corresponding triflates. More importantly, tosylates are more stable towards hydrolysis than are triflates. However, this greater stability renders tosylates less reactive in transition metal-catalyzed coupling reactions. As a result, protocols for traditional cross-coupling reactions of these electrophiles were only recently developed [1], In contrast, catalytic direct arylations with aryl tosylates were not reported previously. However, a ruthenium complex derived from heteroatom substituted secondary phosphine oxide (HASPO) preligand 72 [81] allowed for direct arylations with both electron-deficient, as well... 

Aryl chlorides are important starting materials in palladium-catalyzed coupling reactions [7]. Compared with the corresponding aryl iodides or aryl bromides, the advantages of aryl chlorides are obviously that they are inexpensive, easy to prepare, stable, etc. The same is true if we compare aryl tosylates or aryl mesylates with their aryl triflates analogs. Even though aryl chlorides, aryl mesylates and aryl acetates have been studied and have succeeded in cross-coupling reactions, their... 

Nickel(O) complexes tend to undergo oxidative addition of aryl halides faster than palladium(O) complexes. There are some drawbacks to the use of the nickel complexes, described above, that can outweigh the lower cost of nickel. Nevertheless, the ruckel complexes containing triarylphosphines do undergo oxidative addition of aryl chlorides (Equation 19.39) and tosylates (Equation 19.40), and some mild conditions have been developed for nickel-catalyzed cross couplings of aryl chlorides and aryl tosylates with ligands such as triphenylphosphine or tricyclohexylphosphine. ... 

Aryl bromides are the most reactive aryl halide, and aryl chlorides are the next most reactive for this catalytic process. For reasons not well understood, aryl iodides tend to be less reactive toward palladium-catalyzed cross-couplings that form C-N bonds. " Aryl triflates also couple with amines, - and even the less-reactive aryl tosylates have been shown to couple with amines. " ... 

GooBen, L. J., Rodriguez, N., Lange, P. P., Linder, C. (2010). Decarboxylative cross-coupling of aryl tosylates with aromatic carboxylate salts. Angewandte Chemie International Edition, 49, 1111-1114. 

Scheme 3.19 Decarboxylative cross-coupling of aryl tosylates with aromatic carboxylate salts, as described by Goossen and coworkers [35].

Secondary phosphine oxides have been used in nickel-catalyzed cross-coupling reactions with aryl tosylates and mesylates for the preparation of arylphosphine oxides (Scheme 4.205) [341], These substrates are typically more stable than aryl triflates and can be readily prepared from a wide range of phenols. In terms of the metal catalyst, the authors used a discrete species ((dppONiCl ) and added extra supporting ligand (2 equiv per metal center) to prevent catalyst decomposition. The addition of zinc dust was essential to the success of the reaction, and no arylphosphine oxide was observed without it. 

Cross-Coupling Reaction of 2-(2-Hydroxyprop-2-yl)cyclohexyl-Substituted Arylsilanes with Aryl Tosylates A General Procedur ... 

NiCl2(PCy3)2 associated with PCyj promotes the selective cross-coupling of aryl-tosylates with arylboronic acids under relatively mild conditions, and a variety of function groups are tolerated in both arenes [70]. It is particularly noteworthy that no reducing agent such as Zn is required in this reaction. More recently, room-temperature nickel-catalyzed Suzuki coupling reactions of arenesulfonates with arylboronic acids have been disclosed [71]. 

TABLE 6. Cross-coupling between alkyl Grignard reagents and aryl or heteroaryl chlorides, triflates, and tosylates... 

The Suzuki coupling of aryl halides was also extended to tosylates recently. Benzothiazole 5-tosylate reacted with m-xylene-2-boronic acid (6.13.) to give the coupled product in 94% yield using palladium acetate and a stericly congested biphenyl based phosphine ligand as catalyst.17 Another class of less commonly utilised cross-coupling partners are methyltio derivatives. In the presence of a copper salt, which activates the carbon-sulphur bond, 2-methyltio-benzotiazol coupled readily with a series of arylboronic acids.18... 

One of the challenges in the Suzuki-type cross-coupling is to extend this reaction from electron-rich aryl iodides, bromides, and triflates to less reactive aryl sulfonates and aryl chlorides, which show poor reactivity in terms of oxidative addition in the catalytic cycle. Aryl mesylates, benzenesulfonates, and tosylates are much less expensive than triflates, and are unreactive toward palladium catalysts. The Ni(0)-catalyzed Suzuki-type cross-coupling reaction of aryl sulfonates, including mesylates, with arylboronic acids in the presence of K3P04 has been reported [123]. 

Stereospecific cross-couplings of E- and Z-tosylates 5.44 and 5.46 with aryl boronic acids in the presence of PdCl2(PPh3)2 and aqueous Na2C03 in THF gave the corresponding trisubstituted E- and Z-a,(3-unsaturated esters 5.45 and 5.47, respectively. 

Many transmetalation reactions take place as part of a catalytic cycle. For example, aryl (as well as heterocychc and vinyl) halides, tosylates, and triflates form biaryls with numerous aryl-metal partners. The cross-couphng reactions (which are increasingly being used to prepare other products besides biaryls) are usually named after... 

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