Aryl triflates, Suzuki reaction

ArSnRs, and with arylmercury compounds. Aryl triflates react with arylbo-ronic acids ArB(OH)2, or with organoboranes, in the presence of a palladium catalyst, to give the arene in what is called Suzuki couplingCyclopropyl groups can be attached to aromatic rings by this reaction. Even hindered boronic acids give good yields of the coupled product. 

Stille coupling was also developed in tlie early 1980s and is similar to Suzuki coupling in its sequence. It is used to couple aryl or vinyl halides or triflates with organotin compounds via oxidative addition, transmetallation, and reductive elimination. The oxidative addition reaction has tlie same requirements and preferences as discussed earlier for tlie Heck and Suzuki reactions. The reductive elimination results in formation of tlie new carbon-carbon bond. The main difference is that tlie transmetallation reaction uses an organotin compound and occurs readily without the need for an oxygen base. Aryl, alkenyl, and alkyl stannanes are readily available. Usually only one of tlie groups on tin enters into... 

Palladium catalysts have been found which are effective in the Suzuki coupling reaction of arylboronic acids with aryl chlorides carrying electron-withdrawing groups.73 Biaryls may also be synthesized by cross-coupling of arylboronic acids with arenediazonium salts.74,75 There has been a report of the polymer-bound palladium-catalysed Suzuki coupling of aryl triflates with organoboron compounds.76 Arylbor-onates may themselves be synthesized by the palladium-catalysed reactions of... 

The Suzuki coupling reaction is a powerful tool for carbon-carbon bond formation in combinatorial library production.23 Many different reaction conditions and catalyst systems have been reported for the cross-coupling of aryl triflates and aromatic halides with boronic acids in solution. After some experimentation, we found that the Suzuki cleavage of the resin-bound perfluoroalkylsulfonates proceeded smoothly by using [l,l -bis (diphenylphosphino)ferrocene]dichloropalladium(II), triethylamine, and boronic acids in dimethylformamide at 80° within 8 h afforded the desired biaryl compounds in good yields.24 The desired products are easily isolated by a simple two-phase extraction process and purified by preparative TLC to give the biaryl compounds in high purity, as determined by HPLC, GC-MS, and LC-MS analysis. 

The use of aryl triflates or other sulfonates in the amine arylation reaction is highly desirable from a synthetic standpoint since a large variety of phenols are easily accessed and derivatized. Aryl and vinyl triflates have enjoyed great utility in other Pd-catalyzed transformations such as the Stille [77] and Suzuki [78] couplings, and the Heck [79] reaction. 

Alkylboronic acids and arylboronic acids, RB(OH)2, and ArB(OH)2, respectively, are increasingly important in organic chemistry. The palladium catalyzed coupling reaction of aryl halides and aryl triflates with arylboronic acids (the Suzuki-Miyaura... 

Different conditions (including additives and solvent) for the reaction have been reported,often focusing on the palladium catalyst itself," or the ligand." Catalysts have been developed for deactivated aryl chlorides," and nickel catalysts have been used." Modifications to the basic procedure include tethering the aryl triflate or the boronic acid to a polymer, allowing a polymer-supported Suzuki reaction. Polymer-bound palladium complexes have also been used." " The reaction has been done neat on alumina," and on alumina with microwave irradiation." Suzuki coupling has also been done in ionic liquids," in supercritical... 

Suzuki couplings. Pd-catalyzed reactions of B-allyl borate complex derived from 6-methoxy-9-borabicyclo[3.3.1]nonane with aryl triflates give allylarenes. This technique broadens the scope of the Suzuki coupling to allow transfer of Me, TMSCHj, and alkynyl groups which has eluded conventional manipulations. 

Application of immobilized palladium catalyst under the action of MW, with phase-transfer agents, has also been reported to promote the Suzuki reactions of a range of aryl halides and triflates in solvents such as water and ethanol under MW conditions [120, 121]. Similar results were obtained when aryl halides were attached to a PEG matrix as para-substituted benzoates [122]. It was found that conventional thermal conditions induced up to 45% cleavage of the benzoates whereas this side reaction was suppressed when MW conditions were employed. 

Aldous and co-workers also reported extensive results on palladium-catalyzed coupling reactions. They introduced the utility of electron-deficient pyridazinyl triflate 136 in Stille and Suzuki biaryl cross-couplings with electron rich aryl stannanes and aryl boronales 137 <01SL150>. Electron deficient aryl stannanes resulted in more sluggish reactions and poor yields. In general, Suzuki reactions were found to be better than the corresponding Stille couplings. 

Under noncompetitive conditions, Greaney functionalized C2-chlorides or C4-triflates with a variety of aryl and heteroaryl boronic acids. The authors attempted Suzuki reactions with the C2-sulfonates but found facile thermal decomposition with both triflates and nonaflates. ... 

Table 7. The Suzuky-Miyaura reactions of arylboronic acids with aryl triflates, mesylates and tosylates...

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