Ni 催化的 C(sp3)-O 键活化提供了一种有用的方法来从容易获得的对映体富集的苯甲醇衍生物合成对映体富集的产品。立体特异性的控制是这些转化成功的关键。为了阐明 Ni 催化的熊田和与苄醚的交叉亲电偶联反应的反向立体特异性和化学选择性,进行了计算和实验相结合的研究,以达成统一的机理理解。熊田耦合通过经典的交叉耦合机制进行。初始速率决定氧化加成伴随苄基立体中心的立体反转发生。随后用格氏试剂进行金属转移和顺式还原消除产生熊田偶联产物,在苄基位置具有整体立体反转。交叉亲电偶联反应以相同的苄基 CO 键裂解和金属转移开始,以形成常见的苄基镍中间体。然而,系链烷基氯的存在允许苄基镍部分轻松进行分子内 SN2 攻击。这一步避免了竞争性的熊田偶联,导致交叉亲电偶联的优异化学选择性。这些机制解释了观察到的熊田和交叉亲电偶联的立体特异性,为交叉亲电偶联中苄基立体中心的双重反转提供了基本原理。改进的机械理解将能够设计涉及
Dialkyl Ether Formation by Nickel‐Catalyzed Cross‐Coupling of Acetals and Aryl Iodides
作者:Kevin M. Arendt、Abigail G. Doyle
DOI:10.1002/anie.201503936
日期:2015.8.17
A new substrate class for nickel‐catalyzed C(sp3) cross‐coupling reactions is reported. α‐Oxy radicals generated from benzylic acetals, TMSCl, and a mild reductant can participate in chemoselective cross‐coupling with aryliodides using a 2,6‐bis(N‐pyrazolyl)pyridine (bpp)/Ni catalyst. The mild, base‐free conditions are tolerant of a variety of functional groups on both partners, thus representing
Parameterization of phosphine ligands demonstrates enhancement of nickel catalysis via remote steric effects
作者:Kevin Wu、Abigail G. Doyle
DOI:10.1038/nchem.2741
日期:2017.8
Ligand development underlies many advances in Pd-catalysed cross coupling but has seen limited application in the growing field of Ni catalysis. Now, a phosphine framework is shown to enable Ni-catalysed Suzuki coupling of acetals. Parameterization studies provide structural insight into ligand success and a quantitative model to facilitate further ligand design.
Putting corannulene in its place. Reactivity studies comparing corannulene with other aromatic hydrocarbons
作者:Stephen R. D. George、Thomas D. H. Frith、Donald S. Thomas、Jason B. Harper
DOI:10.1039/c5ob01215e
日期:——
A series of aromatichydrocarbons were investigated so as to compare the reactivity of corannulene with planar aromatichydrocarbons. Corannulene was found to be more reactive than benzene, naphthalene and triphenylene to Friedel–Crafts acylation whilst electrophilicaromatic bromination was also used to confirm that triphenylene was less reactive than corannulene and that pyrene, perylene and acenaphthene
Transition-Metal-Free Cross-Coupling of Acetals and Grignard Reagents To Form Diarylmethyl Alkyl Ethers and Triarylmethanes
作者:Shi-Liang Shi、Yang Qin、Sheng Liu
DOI:10.1055/a-2088-5000
日期:2024.2
reaction of acetals and Grignard reagents. The method provides a modular preparation of diarylmethyl alkyl ethers, triarylmethanes, and 1,1-diarylalkanes that constitute the core structures of many bioactive molecules and synthetic motifs. A series of readily accessible acetals bearing aryl, alkenyl, and alkyl substituents efficiently coupled with commercially available aryl, alkyl, and allylic magnesium
Photoinduced zirconocene catalysis was utilized to achieve the reductivecoupling of ethers with remarkable activity and cross-selectivity. Mechanistic investigation revealed that photoexcitation of low-valent zirconocene facilitates the scission of benzylic C(sp3)−O bonds, resulting in benzylic radicals that recombine with Zr center. Subsequent carbomagnesiation generates benzylic Grignard reagents