[4+2] Annulation of 3-(2,2-diethoxyethyl)-1,3-dicarbonyl compounds with indoles catalyzed by Brønsted acid ionic liquid for the synthesis of carbazoles

Synthesis of Indoles from o-Haloanilines

“…37 mg (70%) as a brown waxy solid by flash column chromatography using hexane/EtOAc (9:1); R f 0.4 (hexane/ EtOAc 9:1); 1 H NMR (CDCl 3 ): δ 7.34 (dd, J = 16.8, 8.5 Hz, 4H), 7.16 (d, J = 8.5 Hz, 1H), 7.13−7.08 (m, 2H), 6.70 (d, J = 8.5 Hz, 1H), 5.77 (s, 1H), 5.55 (s, 1H), 5.35 (s, 1H), 4.69 (s, 1H), 2.35−2.16 (m, 4H), 1.68 (s, 3H), 1.66 (s, 3H), 1.24 (s, 3H), 1.22 (s, 3H), 1.14 (s, 3H) 1.12 (s, 3H); 13 Indoles 5i + 5i′. 29 33 mg (in 57 and 22% yields) as a yellow waxy solid by flash column chromatography using hexane/EtOAc (9:1); R f 0.4 (hexane/EtOAc 9:1); for 5i: 1 H NMR (CDCl 3 ): δ 8.16 (br s, 1H), 7.55 (d, J = 7.8 Hz, 1H), 7.35 (d, J = 8.1 Hz, 1H), 7.19 (m, 1H), 7.12 (m, 1H), 4.26 (q, J = 7.1 Hz, 2H), 2.84 (m, 1H), 2.77 (s, 3H), 2.50−2.48 (m, 3H), 1.36 (t, J = 7.1 Hz, 3H); 13 Indole 5j. 30 19 mg (78%) as a white solid by flash column chromatography using hexane/EtOAc (9:1); R f 0.4 (hexane/EtOAc 9:1); 1 H NMR (CDCl 3 ): δ 7.87 (br s, 1H), 7.59 (d, J = 7.9 Hz, 1H), 7.35 (d, J = 8.0 Hz, 1H), 7.19 (ddd, J = 8.0, 7.0, 1.3 Hz, 1H), 7.12 (ddd, J = 7.9, 7.0, 1.1 Hz, 1H), 6.97 (m, 1H), 2.34 (s, 3H); 13 C{ 1 H} NMR (CDCl 3 ): δ 136.5, 128.5, 122.0, 121.7, 119.3, 119.0, 111.9, 111.1, 9.8.…”

Recent Studies of Bifunctionalization of Simple Indoles

“…The Han group [9a] used the Brønsted acid ionic liquid [BPy]HSO 4 as the catalyst during the cyclization of indoles with 3‐(2,2‐diethoxyethyl)‐1,3‐dicarbonyls. Neither metal catalyst nor exogenous additive were required.…”

Aqueous Extract of Dillenia indica Fruit (AEDI): A Sustainable Biocatalyst for the Synthesis of Pharmacologically Important Bis(indolyl)methanes

“…[1,2] It is predicted that the new class of organic molecules, which are important for biological and medicinal purposes, will be synthesized using a less complex, more environmentally friendly process. Therefore, organic chemists are focusing more on the use of enzymes, [3][4][5] surfactants, [6][7][8][9][10] ionic liquids, [11][12][13][14] supercritical solvents, [15][16][17][18] natural and biodegradable substances [19][20][21][22] as catalysts in synthetic processes.…”