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Carbocation Catalyzed Bromination of Alkyl Arenes, a Chemoselective sp3 vs. sp2 C−H functionalization.
Advanced Synthesis & Catalysis ( IF 5.4 ) Pub Date : 2018-09-13 , DOI: 10.1002/adsc.201800788
Shengjun Ni 1 , Mahmoud Abd El Aleem Ali Ali El Remaily 1, 2 , Johan Franzén 1
Affiliation  

The versatility of the trityl cation (TrBF4) as a highly efficient Lewis acid organocatalyst is demonstrated in a light induced benzylic brominaion of alkyl‐arenes under mild conditions. The reaction was conducted at ambient temperature under common hood light (55 W fluorescent light) with catalyst loadings down to 2.0 mol% using N‐bromosuccinimide (NBS) as the brominating agent. The protocol is applicable to an extensive number of substrates to give benzyl bromides in good to excellent yields. In contrast to most previously reported strategies, this protocol does not require any radical initiator or extensive heating. For electron‐rich alkyl‐arenes, the trityl ion catalyzed bromination could be easily switched between benzylic sp3 C−H functionalization and arene sp2 C−H functionalization by simply alternating the solvent. This chemoselective switch allows for high substrate control and easy preparation of benzyl bromides and bromoarenes, respectively. The chemoselective switch was also applied in a one‐pot reaction of 1‐methylnaphthalene for direct introduction of both sp3 C−Br and sp2 C−Br functionality.

中文翻译:

碳氢化合物催化烷基芳烃的溴化,sp3 vs.sp2 CHH的化学选择性。

在温和的条件下,光诱导的烷基芳烃的苄基溴化反应证明了三苯甲基阳离子(TrBF 4)作为高效的路易斯酸有机催化剂的多功能性。使用N-溴代琥珀酰亚胺(NBS)作为溴化剂,该反应在环境温度下于普通遮光罩(55 W荧光灯)下进行,催化剂负载量低至2.0 mol%。该方案适用于多种底物,以高至极好的收率得到苄基溴。与大多数以前报道的策略相反,该协议不需要任何自由基引发剂或大量加热。对于富含电子的烷基芳烃,三苯甲基离子催化的溴化反应可轻松地在苄基sp 3 CH功能和芳烃之间切换通过简单地交替使用溶剂即可实现sp 2 CH功能化。这种化学选择性开关可实现较高的底物控制,并易于分别制备苄基溴和溴芳烃。化学选择性开关还用于1-甲基萘的一锅反应中,以直接引入sp 3 C-Br和sp 2 C-Br官能团。
更新日期:2018-09-13
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