脱氢[4 + 2]环化是构建苯并稠合六元环的一种步骤和原子经济的方法,苯并稠合六元环在天然产物、药物和农用化学品中普遍存在。在此,我们公开了苯并硫酰胺和炔烃的可见光诱导脱氢[4 + 2]成环反应,该反应在温和有氧条件下进行,并由无金属异质光催化剂石墨氮化碳(gC 3 N 4)催化。多相光催化操作简单、条件温和,进展顺利,并以良好的收率产生了多种异硫色烯。gC 3 N 4在光化学反应中表现出优异的稳定性和可回收性。详细的机制研究表明,gC3 N 4在可见光照射下通过单电子转移过程促进了以硫为中心的自由基的形成。自由基中间体进一步介导与炔烃的[4+2]环化,产生异硫色烯。
Exogenous Photosensitizer-, Metal-, and Base-Free Visible-Light-Promoted C–H Thiolation via Reverse Hydrogen Atom Transfer
作者:Ze-Ming Xu、Hong-Xi Li、David James Young、Da-Liang Zhu、Hai-Yan Li、Jian-Ping Lang
DOI:10.1021/acs.orglett.8b03679
日期:2019.1.4
This reaction induces the cyclization of thiobenzanilides to benzothiazoles. The substrate absorbs visible light, and its excited state undergoes a reverse hydrogen-atom transfer (RHAT) with 2,2,6,6-tetramethylpiperidineN-oxyl to form a sulfur radical. The addition of the sulfur radical to the benzene ring gives an aryl radical, which then rearomatizes to benzothiazole via RHAT.
Three-componentreactions involving amines, aldehydes, and elemental sulfur powder are reported to afford thioamides in a simple one-pot procedure in the absence of a catalyst. A variety of thioamides can be obtained in good to excellent yields up to 88 %.
An aerobic visible-light driven photoredox catalytic formation of 2-substitutedbenzothiazoles through radical cyclization of thioanilides has been accomplished. The reaction features C–H functionalization and C–S bond formation with no direct metal involvement except the sensitizer. The reaction highlights the following: (1) visible-light is the reaction driving force; (2) molecular oxygen is the
Use of Molecular Oxygen as a Reoxidant in the Synthesis of 2-Substituted Benzothiazoles via Palladium-Catalyzed CH Functionalization/Intramolecular CS Bond Formation
作者:Kiyofumi Inamoto、Chisa Hasegawa、Junpei Kawasaki、Kou Hiroya、Takayuki Doi
DOI:10.1002/adsc.201000604
日期:2010.10.4
Molecularoxygen (O2) was successfully employed as a reoxidant in cyclizations of thiobenzanilides 1a–s through a palladium-catalyzed CH functionalization/intramolecular CS bondformation process, leading to an efficient, green method for the synthesis of 2-arylbenzothiazoles 2a–s. Addition of cesium fluoride (CsF) greatly enhanced the reactions, which produced variously substituted 2-arylbenzothiazoles
Palladium-Catalyzed C-H Cyclization in Water: A Milder Route to 2-Arylbenzothiazoles
作者:Kiyofumi Inamoto、Yoshinori Kondo、Kanako Nozawa
DOI:10.1055/s-0031-1291164
日期:2012.7
medium in palladium-catalyzed C–H cyclization of thiobenzanilides. Reactions efficiently proceeded under considerably mild conditions such as 40 °C in water, providing a more practical, greener method for the synthesis of 2-arylbenzothiazoles. For somesubstrates, the addition of an amphiphilic surfactant greatly enhanced the process. The method represents a rare example of palladium-catalyzed C–H functionalization
在钯催化的硫代苯甲酰苯胺的 C-H 环化中,水被成功用作反应介质。反应在相当温和的条件下有效进行,例如在 40 °C 的水中,为合成 2-芳基苯并噻唑提供了一种更实用、更环保的方法。对于某些基材,添加两亲性表面活性剂大大增强了该过程。该方法代表了在水中进行钯催化的 C-H 功能化过程的一个罕见例子。