Mechanistic Investigations of Cooperative Catalysis in the Enantioselective Fluorination of Epoxides
作者:Julia A. Kalow、Abigail G. Doyle
DOI:10.1021/ja207256s
日期:2011.10.12
studies of the (salen)Co- and amine-cocatalyzed enantioselective ring opening of epoxides by fluoride. The kinetics of the reaction, as determined by in situ (19)F NMR analysis, are characterized by apparent first-order dependence on (salen)Co. Substituent effects, nonlinear effects, and reactivity with a linked (salen)Co catalyst provide evidence for a rate-limiting, bimetallic ring-opening step. To account
本报告描述了(salen)Co 和胺共催化的环氧化物对映选择性开环的机理研究。通过原位 (19)F NMR 分析确定的反应动力学特征在于对 (salen)Co 的明显一级依赖性。取代基效应、非线性效应和与连接的 (salen) Co 催化剂的反应性为限速双金属开环步骤提供了证据。为了解释这些不同的数据,我们提出了一种机制,其中活性亲核氟物质是形成静止状态二聚体的氟化钴。胺助催化剂与 (salen) Co 的轴向连接促进二聚体解离,并且是观察到的协同性的起源。在这些研究的基础上,我们表明在比率、周转次数、氟化物开环反应的底物范围可以通过使用连接的salen框架来实现。报道了将该催化剂系统应用于快速(5 分钟)氟化以生成已知 PET 示踪剂 F-MISO 的未标记类似物。
Two-Step, Practical, and Diversity-Oriented Synthesis of Multisubstituted Benzofurans from Phenols through Pummerer Annulation Followed by Cross-coupling
作者:Kei Murakami、Hideki Yorimitsu、Atsuhiro Osuka
DOI:10.1246/bcsj.20140241
日期:2014.12.15
Practical and diversity-oriented synthesis of multisubstituted benzofurans has been accomplished from simple phenols through a Pummerer annulation/cross-coupling sequence. Operationally simple and rapid reactions of phenols with ketene dithioacetal monoxides (KDMs) with the aid of trifluoroacetic anhydride provide the corresponding 2-methylsulfanylbenzo[b]furans. The scope of the reaction encompasses phenols and KDMs having a broad range of substituents. The remaining methylsulfanyl group in the annulation products is converted to various aryl groups through cross-coupling reactions that we improved specially to this end. This two-step approach to multisubstituted benzofurans is powerful enough to synthesize highly fluorescent benzofuran derivatives as well as the naturally occurring Eupomatenoid family.
Enantioselective epoxidation of cyclic 1,3-dienes catalyzed by a sterically and electronically optimized (salen)Mn complex
作者:Sukbok Chang、Richard M Heid、Eric N Jacobsen
DOI:10.1016/s0040-4039(00)75786-8
日期:1994.1
Chiral (salen)Mn(III)Cl complexescatalyze epoxidation of cyclic 1,3-dienes with moderate-to-good enantioselectivity. A new catalyst (2), bearing sterically hindered and electrondonating OSi(iPr)3 (OTIPS) substituents, induces up to 12% higher selectivity than the previously-reported tert-butyl substituted analog 1.