Catalytic Hydroetherification of Unactivated Alkenes Enabled by Proton‐Coupled Electron Transfer
作者:Elaine Tsui、Anthony J. Metrano、Yuto Tsuchiya、Robert R. Knowles
DOI:10.1002/anie.202003959
日期:2020.7.13
We report a catalytic, light‐driven method for the intramolecular hydroetherification of unactivated alkenols to furnish cyclic ether products. These reactions occur under visible‐light irradiation in the presence of an IrIII‐based photoredox catalyst, a Brønsted base catalyst, and a hydrogen‐atom transfer (HAT) co‐catalyst. Reactive alkoxy radicals are proposed as key intermediates, generated by direct
我们报告了一种催化光驱动方法,用于未活化烯醇的分子内加氢醚化以提供环醚产品。这些反应在 Ir III基光氧化还原催化剂、布朗斯台德碱催化剂和氢原子转移 (HAT) 助催化剂存在下在可见光照射下发生。反应性烷氧基被认为是关键中间体,是通过质子耦合电子转移机制直接均裂激活醇 O−H 键而产生的。该方法表现出广泛的底物范围和高官能团耐受性,并且适应多种烯烃取代模式。还提出了证明该催化系统扩展到碳醚化反应的结果。
Enantioselective Hydroamination of Alkenes with Sulfonamides Enabled by Proton-Coupled Electron Transfer
作者:Casey B. Roos、Joachim Demaerel、David E. Graff、Robert R. Knowles
DOI:10.1021/jacs.0c01332
日期:2020.4.1
proceed via N-centered radicals formed by proton-coupled electron transfer (PCET) activation of sulfonamide N-H bonds. Non-covalent interactions between the neutral sulfonamidyl radical and a chiral phosphoric acid generated in the PCET event are hypothesized to serve as the basis for asymmetric induction in a subsequent C-N bond forming step, achieving selectivities of up to 98:2 er. These results offer
报道了一种对映选择性、基于自由基的方法,用于烯烃与磺酰胺的分子内加氢胺化。建议这些反应通过磺酰胺 NH 键的质子耦合电子转移 (PCET) 活化形成的 N 中心自由基进行。中性磺酰胺自由基与 PCET 事件中产生的手性磷酸之间的非共价相互作用被假设为后续 CN 键形成步骤中不对称诱导的基础,实现高达 98:2 er 的选择性。这些结果进一步支持了非共价相互作用在瞬态和高反应性开壳中间体的反应中增强立体选择性的能力。
Modular Design of Chiral Conjugate-Base-Stabilized Carboxylic Acids: Catalytic Enantioselective [4 + 2] Cycloadditions of Acetals
Readily available 1,2-amino alcohols provide the framework for a new generation of chiral carboxylicacid catalysts that rival the acidity of the widely used chiral phosphoric acid catalyst (S)-TRIP. Covalently linked thiourea sites stabilize the carboxylate conjugate bases of these catalysts via anion-binding, an interaction that is largely responsible for the low pKa values. The utility of the new
Secondary Products from Intramolecular Cycloadditions of Azidoalkyl Enol Ethers and Azidoalkyl Vinyl Bromides: 1-Azadienes, Their Reactions with Diphenylketene, and Radical Cyclizations To Form Bi- and Tricyclic Lactams
作者:John T. R. Liddon、Peter J. Lindsay-Scott、Jeremy Robertson
DOI:10.1021/acs.joc.9b02005
日期:2019.11.1
cycloadducts formed by heating analogous azidoalkyl vinyl bromides are unstable with respect to elimination of N2 and HBr, affording 1-azadienes (2-alkenyl cyclic imines). These primary products may be isolated or treated directly with diphenylketene to produce bi- and tricyclic 3,4-dihydropyridin-2(1H)-ones; similar ring systems may also be produced from the azadienes by N-acylation and radical cyclization