17637-72-8Relevant articles and documents
Preparation of Secondary Phosphine Oxide Ligands through Nucleophilic Attack on Imines and Their Applications in Palladium-Catalyzed Catellani Reactions
Hu, Chan-Yu,Chen, Ya-Qian,Lin, Guan-Yu,Huang, Ming-Kai,Chang, Yu-Chang,Hong, Fung-E
, p. 3131 - 3142 (2016)
Several new amino-type secondary phosphine oxide (SPO) pre-ligands (3a–3h) that contain P–N bonds were synthesized and characterized. SPOs 3a–3h can tautomerize to phosphinous acids (PA, 3a–3h) as genuine ligands. The formation of SPOs 3a–3h occurred first through nucleophilic attack on the imine carbon atom, then by the addition of RPCl2(R = Ph, Cy, tBu, or iPr), and work-up under acidic conditions. The P–N bond in the newly prepared SPOs is evident from the crystal structures of SPOs 3d and 3h. Reactions of SPOs 3f, 3g, or 3h with Pd(COD)Cl2(COD = cyclooctadiene) yielded palladium complexes 6f, 6g, or 6h. In these crystal structures, PAs 3f, 3g, and 3h act as didentate ligands through P and N donors. Intriguingly, the reaction of SPO 3f with Pd(COD)Cl2also gave rise to palladium complexes 7fa, 7fb, and 8f. The crystal structures of 7fa and 7fb show that the palladium atom is chelated by PA 3f and coordinated by a phosphine-like ligand fragmented from SPO 3f through C–N bond dissociation. Finally, the syntheses of carbazole derivatives were pursued in Catellani reactions with SPOs 3g and 3h as pre-ligands. A mechanism is proposed to account for the catalytic reaction (see the Supporting Information). The optimized conditions for Suzuki reactions using selected SPO ligands are also reported.
Insight into the Modes of Activation of Pyridinium and Bipyridinium Salts in Non-Covalent Organocatalysis
Weiss, Robin,Golisano, Tamara,Pale, Patrick,Mamane, Victor
supporting information, p. 4779 - 4788 (2021/09/06)
A series of pyridinium and bipyridinium salts were prepared and their catalytic properties were evaluated in the aza-Diels-Alder reaction between imines and Danishefsky diene. Depending on the substituents of the pyridinium/bipyridinium rings and on the nature of the counterion, two mechanisms of activation were demonstrated. In case of non-substituted rings, the substrate is activated through charge transfer involving the aryl ring on the C-side of the imine. When halogen atoms were introduced on the catalysts, the activation mode switched to halogen bond involving the imine nitrogen lone pair. Moreover, alternative activation modes based on hydrogen bonding and radical cation were ruled out. This work allowed us to develop two families of catalysts whose potential was demonstrated in the cycloaddition of various imines with Danishefsky diene. The first family is composed of the simple methyl pyridinium triflate and dioctyl bipyridinium triflate. The former is active only with imines bearing a p-methoxyphenyl group on the C-side and the latter was found to be efficient with imines bearing different substituents on both the N- and C-sides of the imines. The second family is based on halogenated pyridinium salts which proved active with almost all considered imines. (Figure presented.).
Metal-free regioselective C-H amination for the synthesis of pyrazole-containing 2H-indazoles
Wang, Kai,Wei, Tingting,Zhang, Yujia,Hou, Jiahao,Bai, Renren,Xie, Yuanyuan
, p. 1787 - 1794 (2021/03/14)
A general and practical regioselective approach for the C-H amination of 2H-indazoles under transition-metal-free conditions was developed. A series of substrates were tested showing eminent functional group tolerance and affording the C-N functionalization products in good to excellent yields. Mechanism studies revealed that a radical process was involved in this transformation.