214360-46-0Relevant articles and documents
Improvement in the Palladium-Catalyzed Miyaura Borylation Reaction by Optimization of the Base: Scope and Mechanistic Study
Barroso, Santiago,Joksch, Markus,Puylaert, Pim,Tin, Sergey,Bell, Stephen J.,Donnellan, Luke,Duguid, Stewart,Muir, Colin,Zhao, Peichao,Farina, Vittorio,Tran, Duc N.,De Vries, Johannes G.
supporting information, p. 103 - 109 (2020/12/22)
Aryl boronic acids and esters are important building blocks in API synthesis. The palladium-catalyzed Suzuki-Miyaura borylation is the most common method for their preparation. This paper describes an improvement of the current reaction conditions. By using lipophilic bases such as potassium 2-ethyl hexanoate, the borylation reaction could be achieved at 35 °C in less than 2 h with very low palladium loading (0.5 mol %). A preliminary mechanistic study shows a hitherto unrecognized inhibitory effect by the carboxylate anion on the catalytic cycle, whereas 2-ethyl hexanoate minimizes this inhibitory effect. This improved methodology enables borylation of a wide range of substrates under mild conditions.
Unveiling Extreme Photoreduction Potentials of Donor-Acceptor Cyanoarenes to Access Aryl Radicals from Aryl Chlorides
Cao, Jilei,Tang, Xinxin,Toh, Ren Wei,Wang, Han,Wu, Jie,Wu, Xiangyang,Xu, Jinhui,Yang, Xiaona,Yeow, Edwin K. L.,Zhou, Rong
supporting information, p. 13266 - 13273 (2021/09/07)
Since the seminal work of Zhang in 2016, donor-acceptor cyanoarene-based fluorophores, such as 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), have been widely applied in photoredox catalysis and used as excellent metal-free alternatives to noble metal Ir- and Ru-based photocatalysts. However, all the reported photoredox reactions involving this chromophore family are based on harnessing the energy from a single visible light photon, with a limited range of redox potentials from -1.92 to +1.79 V vs SCE. Here, we document the unprecedented discovery that this family of fluorophores can undergo consecutive photoinduced electron transfer (ConPET) to achieve very high reduction potentials. One of the newly synthesized catalysts, 2,4,5-tri(9H-carbazol-9-yl)-6-(ethyl(phenyl)amino)isophthalonitrile (3CzEPAIPN), possesses a long-lived (12.95 ns) excited radical anion form, 3CzEPAIPN?-*, which can be used to activate reductively recalcitrant aryl chlorides (Ered ≈ -1.9 to -2.9 V vs SCE) under mild conditions. The resultant aryl radicals can be engaged in synthetically valuable aromatic C-B, C-P, and C-C bond formation to furnish arylboronates, arylphosphonium salts, arylphosphonates, and spirocyclic cyclohexadienes.
Cleavage of C(aryl)?CH3 Bonds in the Absence of Directing Groups under Transition Metal Free Conditions
Dai, Peng-Fei,Ning, Xiao-Shan,Wang, Hua,Cui, Xian-Chao,Liu, Jie,Qu, Jian-Ping,Kang, Yan-Biao
supporting information, p. 5392 - 5395 (2019/03/29)
Organic chemists now can construct carbon–carbon σ-bonds selectively and sequentially, whereas methods for the selective cleavage of carbon–carbon σ-bonds, especially for unreactive hydrocarbons, remain limited. Activation by ring strain, directing groups, or in the presence of a carbonyl or a cyano group is usually required. In this work, by using a sequential strategy site-selective cleavage and borylation of C(aryl)?CH3 bonds has been developed under directing group free and transition metal free conditions. Methyl groups of various arenes are selectively cleaved and replaced by boryl groups. Mechanistic analysis suggests that it proceeds by a sequential intermolecular oxidation and coupling of a transient aryl radical, generated by radical decarboxylation, involving a pyridine-stabilized persistent boryl radical.
