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Discovery of Oxygen α-Nucleophilic Addition to α,β-Unsaturated Amides Catalyzed by Redox-Neutral Organic Photoreductant
Journal of the American Chemical Society ( IF 15.0 ) Pub Date : 2020-12-02 , DOI: 10.1021/jacs.0c10707
Zi-Hong Luan 1 , Jian-Ping Qu 2 , Yan-Biao Kang 1, 3
Affiliation  

The conjugate additions of oxygen-centered nucleophiles to conjugate acceptors are among the most powerful C-O bond formation reactions. The conjugate addition normally takes place at the β-position carbon to the electron-withdrawing group, resulting in the formation of a stabilized carbanion intermediate that can be quenched by proton or electrophiles to form the β-addition (i.e., hetero-Michael addition) products. On the contrary, the formation of α-hydroxyl or alkoxyl amides through conjugate addition needs an α,β-inverse addition. Nevertheless, a regio-inversed nucleophilic α-addition of oxygen-centered nucleophiles to α,β-unsaturated carbonyl compounds still remains less explored because of the electronic mismatch. In this research, we discovered the first α-specific nucleophilic addition of α,β-unsaturated amides with oxygen and fluoride nucleophiles. This region-inversed nucleophilic addition is enabled by the catalysis of a novel redox-neutral nondonor-acceptor organic photoreductant (CBZ6). As low as 0.5 mol % of visible light photoreductant was employed. The mechanistic insights were also explored. The oxidative potential of the excited state of CBZ6 is obtained in -1.92 V (vs SCE), presenting a stronger reductive potential than representative metal-cored or organic photoredox catalysts. This feature enabled the umpolung of α,β-unsaturated amides to take place α-nucleophilic addition other than the normal β-addition.

中文翻译:

氧化还原-中性有机光还原剂催化α,β-不饱和酰胺的氧α-亲核加成的发现

以氧为中心的亲核试剂与共轭受体的共轭加成是最强大的 CO 键形成反应之一。共轭加成通常发生在吸电子基团的 β 位碳上,导致形成稳定的碳负离子中间体,该中间体可以被质子或亲电试剂淬灭以形成 β-加成(即杂迈克尔加成)产品。相反,通过共轭加成形成α-羟基或烷氧基酰胺需要α,β-逆加成。然而,由于电子失配,以氧为中心的亲核试剂与 α,β-不饱和羰基化合物的区域反转亲核 α-加成仍然很少被探索。在这项研究中,我们发现了第一个 α 特异性亲核加成,β-不饱和酰胺与氧和氟亲核试剂。这种区域反转的亲核加成是通过新型氧化还原中性非供体受体有机光还原剂 (CBZ6) 的催化实现的。使用低至 0.5 mol% 的可见光光还原剂。还探讨了机械方面的见解。CBZ6 激发态的氧化电位在 -1.92 V(vs SCE)下获得,呈现出比代表性金属核或有机光氧化还原催化剂更强的还原电位。这一特征使 α,β-不饱和酰胺的 umpolung 发生 α-亲核加成而不是正常的 β-加成。还探讨了机械方面的见解。CBZ6 激发态的氧化电位在 -1.92 V(vs SCE)下获得,呈现出比代表性金属核或有机光氧化还原催化剂更强的还原电位。这一特征使 α,β-不饱和酰胺的 umpolung 发生 α-亲核加成而不是正常的 β-加成。还探讨了机械方面的见解。CBZ6 激发态的氧化电位在 -1.92 V(vs SCE)下获得,呈现出比代表性金属核或有机光氧化还原催化剂更强的还原电位。这一特征使 α,β-不饱和酰胺的 umpolung 发生 α-亲核加成而不是正常的 β-加成。
更新日期:2020-12-02
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