A series of geometry‐constrained iminopyridyl‐palladium chlorides were synthesized and characterized. These phosphine‐free palladium complexes were explored for their catalytic activities in both Suzuki and Heck cross‐coupling reactions, achieving turnover numbers as high as 106 towards various aryl bromides, even those containing various functionalities. In addition, the influence of substituents with steric and electronic factors was reflected by the differences observed in their activities.magnified image
Ah ighly N 2 -regioselective functionalization of 2H-1,2,3-triazole and 1H-1,2,3-triazole was achievedv ia a para-toluenesulfonic-acid-catalyzed olefin hydroamination. The reaction afforded the corresponding products with up to 92 %N 2 regioselectivity. N 2 -substituted 1,2,3-triazoles possessing ab road spectrum of biological activities have been widely used in biological research and medicinal chemistry. [1] Recent studies have also shown that these compounds have strong fluorescencee mission, and are an ew class of UV/blue-light-emitting fluorophores. [2] However,t he difficulty in achieving the N 2 -selective functionalization of 1,2,3-triazolesi saconsequence of the lower electron density at the N 2 -atom than at the N 1 -atom of the triazole heterocycle,which has limited their further application. [3] In this regard,r egioselective synthesis of N 2 -substituted 1,2,3-triazoles is ac hallenging topic in organic synthesis. Several impressivesynthetic strategies such as Pd 0 /Cu I bimetallic catalyzed allylation, [4] Pd 0 - [5] or Cu I - [2a] catalyzed arylation, Rh-catalyzed coupling of benzotriazoles with allenes, [6] Cu II -catalyzed hydroxymethylation, [7] and nucleophilics ubstitution [8] achieved high N 2 -selectivity;h owever,t hese protocols suffered from limited functional groups at the N 2 -site of triazoles, structure-spe-cific substrates such as 4-bromo-NH-1,2,3-triazoles, or the use of transition-metal catalysts.Hydroamination of non-activated olefins under environmentally friendly conditions with high chemo-and regioselectivity remains an intriguing challenge in the synthesis of nitrogencontaining compounds. While progress has been made for metal-catalyzed olefin hydroaminations, drawbacks such as the use of expensive and toxic metals,t he requirement of inert gas atmosphere and tedious reaction procedures still exist. [9] Protonation of the carbon-carbon double bond is well-known as ak ey step in the acid-catalyzed transformations of olefins, [9b] affording the corresponding carbocation intermediates (E È ), which could be attacked by nucleophiles. Weakly basic N-nucleophilc reagents such as anilines, [10] azoles, [11] sulfonamides, [12] and amides [12c] can be processed efficientlyu nder Brønstedacid-catalyzed hydroamination conditions. [13] Encouraged by these results, we wondered if NH-1,2,3-triazole could be used as an itrogen nucleophile in this hydroamination. Moreover, under acidic conditions, the nucleophilicity of two terminal nitrogens of NH-1,2,3-triazoles bearing higher electron density may be blocked, [2a, 7] leadingt or egioselective N 2 -alkylation ( Figure 1). Herein, we report an efficient Brønsted-acid-catalyzed N 2 -regioselective olefin hydroamination and the photonic emissions of N 2 -alkylated 1,2,3-triazoles.Initially,o ptimization reactions of hydroamination of 4phenyl-2H-1,2,3-triazole (1a,0 .2 mmol) with 1-methyl-1-phenylethene (2a,0 .2 mmol) were carriedo ut in the presence of aB rønsted acid catalyst. From the catalyst screening, it was found that strong Brønst...
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