Catalyst- and oxidant-free electrooxidative site-selective [3/4 + 2] annulation to fused polycyclic heteroaromatics

• Published in: Green chemistry : an international journal and green chemistry resource : GC Vol. 24; no. 13; pp. 5191 - 5196
• Main Authors: Guan, Wenjing, Ying, Ke, Yuan, Chengcheng, Hang, Jinlin, Liu, Chengkou, Huang, Xiangxing, Fang, Zheng, Guo, Kai
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 04.07.2022
• Subjects: Adaptability; Alkynes; Aromatic compounds; Atom economy; Catalysts; Chemical reactions; Electrochemical oxidation; Electrochemistry; Functional groups; Green chemistry; Heterocyclic compounds; Labeling; Organic chemistry; Oxidants; Oxidation; Oxidizing agents; Pyridines; Regioselectivity; Substrates; Transition metals
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/d2gc01248k

Annulation π-extension of arenes with alkynes is a straightforward and practical strategy for the rapid construction of polycyclic aromatic compounds. Recently, some intriguing transition-metal-catalyzed polycyclic arene syntheses were described. However, metal catalysts and exogenous oxidants were essential, which led to undesired by-products, low atom-economy and potential explosion risk. Herein, a straightforward electrochemical oxidation [3 + 2] or [4 + 2] annulation of imidazo[1,2- a ]pyridines with alkynes to heterocyclic aromatic compounds under metal- and exogenous oxidant-free conditions has been accomplished. This green and sustainable methodology features excellent regioselectivity, wide substrate adaptability and good functional group compatibility. Moreover, a possible mechanism has been proposed on the basis of radical-trapping, isotope-labelling, KIE and cyclic voltammetry experiments. A catalyst- and oxidant-free electrooxidative site-selective [3/4 + 2] annulation through π-extension to fused polycyclic heteroaromatics has been developed.