Enantioselective Photoredox Catalysis Enabled by Proton-Coupled Electron Transfer: Development of an Asymmetric Aza-Pinacol Cyclization
作者:Lydia J. Rono、Hatice G. Yayla、David Y. Wang、Michael F. Armstrong、Robert R. Knowles
DOI:10.1021/ja4100595
日期:2013.11.27
protocol for the reductive coupling of ketones and hydrazones is reported. These reactions proceed through neutral ketyl radical intermediates generated via a concerted proton-coupled electron transfer (PCET) event jointly mediated by a chiral phosphoric acid catalyst and the photoredox catalyst Ir(ppy)2(dtbpy)PF6. Remarkably, these neutral ketyl radicals appear to remain H-bonded to the chiral conjugate
报道了第一个用于酮和腙还原偶联的高度对映选择性催化方案。这些反应通过由手性磷酸催化剂和光氧化还原催化剂 Ir(ppy)2(dtbpy)PF6 共同介导的协同质子耦合电子转移 (PCET) 事件产生的中性羰基自由基中间体进行。值得注意的是,在随后的 CC 键形成步骤过程中,这些中性羰基自由基似乎保持与布朗斯台德酸的手性共轭碱 H 键合,从而提供具有优异水平的非对映选择性和对映选择性的顺式 1,2-氨基醇衍生物. 这项工作首次证明了不对称催化中协同 PCET 活化的可行性和潜在益处。