Expansion of Azulenes as Nonbenzenoid Aromatic Compounds for C-H Activation: Rhodium- and Iridium-Catalyzed Oxidative Cyclization of Azulene Carboxylic Acids with Alkynes for the Synthesis of Azulenolactones and Benzoazulenes was written by Maeng, Chanyoung;Son, Jeong-Yu;Lee, Seung Cheol;Baek, Yonghyeon;Um, Kyusik;Han, Sang Hoon;Ko, Gi Hoon;Han, Gi Uk;Lee, Kyungsup;Lee, Kooyeon;Lee, Phil Ho. And the article was included in Journal of Organic Chemistry in 2020.Reference of 65350-59-6 This article mentions the following:
Rhodium-catalyzed oxidative [4+2] cyclization reactions through the C-H activation of azulene carboxylic acids as nonbenzenoid aromatic compounds with sym. and unsym. alkynes were developed under aerobic conditions, which produced azulenolactone derivatives with a wide substrate scope and excellent functional group tolerance. Interestingly, azulenic acids in reaction with alkynes underwent iridium-catalyzed [2+2+2] cyclization accompanied by decarboxylation to afford tetra(aryl)-substituted benzoazulene derivatives The reactivity order for C-H activation reaction was greater toward azulene-6-carboxylic acid, azulene-1-carboxylic acid and azulene-2-carboxylic acid. For the first time, the expansion of azulenes having directing group as nonbenzenoid aromatic compounds for C-H activation was successful, indicating that nonbenzenoid aromatic compounds can be used as good substrates for the C-H activation reaction. Therefore, the research area of C-H activation will certainly expand to nonbenzenoid aromatic compounds in future. In the experiment, the researchers used many compounds, for example, 1-Butyl-4-methylpyridin-1-ium bromide (cas: 65350-59-6Reference of 65350-59-6).
1-Butyl-4-methylpyridin-1-ium bromide (cas: 65350-59-6) belongs to pyridine derivatives. Pyridine’s the lone pair does not contribute to the aromatic system but importantly influences the chemical properties of pyridine, as it easily supports bond formation via an electrophilic attack. Halopyridines are particularly attractive synthetic building blocks in a variety of cross-coupling methods, including the Suzuki-Miyaura cross-coupling reaction.Reference of 65350-59-6