Amination of Aryl Triflates

Palladium(O) complexes containing P(o-C6H4Me)3 as ligand show low reactivity toward aryl triflates [95,96]. Thus, the original catalyst is not effective for the ami-nation of aryl triflates. However, palladium complexes with the chelating phosphines DPPF and BINAP are effective [97,98]. Selected animations of aryl triflates by aniline are shown in Eq. (9), and selected animations of aryl triflates by alkylamines in Eq. (10). 

Palladium(O) complexes containing P(o-C6H4Me)3 as a ligand show low reactivity toward aryl triflates [116, 117]. Thus, the original catalyst is not effective for the amination of aryl tri- 

Recently, Torisawa reported that the addition of 18-crown-6 promotes the reactions of aryl triflates when Cs2C03 is used as the base [121]. This study focused on the reactions of N-Boc piperazine. In the absence of the crown ether, bis-N-Boc piperazine was produced as a byproduct, and reaction times were long. Yields for the reaction of 3,4-dichlorophenyl triflate with N-Boc piperazine were 35 % and 65 %, respectively, in the absence and presence of the crown ether. A similar effect was also observed for the reaction of the analogous dichloro bromoarene. 

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Wolfe, J. and Buchwald, S. Palladium-catalyzed amination of aryl triflates. J. Org. Chem. 1997, 62, 1264-1267. 

Other groups have utilized the ( )-BINAP/Pd-catalyst to prepare several interesting products by the amination of aryl triflate precursors. For example, the 3H-naphth[2,l -h]pyran triflate below was coupled in 72 % yield, providing a photochromic material, Eq. (58) [83]... 

Leeuwen and coworkers studied the kinetics for the amination of aryl triflates and bromides using different Xantphos catalyst systems. " For triflate amination, they found the rate to be first order in amine and ferf-butoxide, but zero order in aryl triflate. From this, they concluded that a mechanism similar to the upper pathway in Scheme 7 was operating, with the deprotonation of coordinated amine being the ratedetermining step. For aryl bromides, however, the rate was dependent on the concentration of iert-butoxide, but not amine or aryl bromide. Thus, under these conchtions, the lower pathway-with the replacement of halide by tert-butoxide as the rate-limiting step - was postulated to be the operating mechanism. 

The palladium catalyzed amination of aryl triflates has proved to be a more challenging problem. Aryl triflates are less favored to undergo oxidative addition as compared to aryl bromides and iodides. Another, more daunting, challenge with aryl triflates is their proclivity to react with NaOt-Bu at sulfur to give a sodium phenoxide as the major by-product. Buchwald s laboratory reported that with fairly electron rich (EDG) and neutral aryl triflates, they could use NaO/-Bu as a base with minor amounts of... 

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