Thermal and Microwave‐Assisted Conjugate Additions of Indole on Electron‐Deficient Nitro‐olefins

Catalyst-free aqueous-mediated conjugative addition of indoles to β-nitrostyrenes

“…Whereas b-nitrostyrenes bearing electron-withdrawing groups (Cl, NO 2 ), such as 4-chloro (b-nitrostyrene) (6) and 4-nitro-(b-nitrostyrene) (7), proceed smoothly in short reaction times (6 h and 4 h) to their corresponding indole adducts. Moreover, sterically hindered naphthyl nitroalkene (8) reacted with indole to afford the product (8a) in good yield. It's important to note that the acid-sensitive moieties such as furan (9) and thiophene (10) survived under the present reaction conditions (Table 1).…”

“…However, upon addition of the surfactant (SDS) did not show any improvement in the reaction. 6h Recently, Kusurkar group have described catalyst-free Michael addition of b-nitrostyrene with indole at 120-140°C in benzene in 48 h. 8 It has been proven that water acts as an acid at elevated temperature in different reactions. 9 Recently, many of the acid-catalyzed reactions were carried out successfully without any catalyst in aqueous medium.…”

Montmorillonite K10–Catalyzed Michael Addition of Indoles to Nitroolefins Under Solvent-Free Conditions

“…A variety of methods have been explored for the Michael addition reaction of indoles with a,b-substituted acceptors in the presence of protic or Lewis acids for the preparation of substituted indoles. [4][5][6][7][8][9][10][11][12][13][14][15] Nowadays, the ''greening'' of global chemical processes has become a major issue in chemical research. [16] While designing a new methodology under investigation, chemists always keep in mind the legislation on environmental friendliness in synthetic pathways and processes to prevent waste, avoid the use of auxiliary substances (e.g., solvents, separation agents), and minimize the potential for chemical accidents (e.g., explosion, fire).…”

An efficient and clean Michael addition of indoles to electron‐deficient olefins under solvent‐ and catalyst‐free condition

“…However, these catalysts still appeared to have several shortcomings, for example, toxicity of metal salts. Recently, catalyst‐free Michael addition of nitrostyrene with indole was developed [31, 32]. However, the reaction required higher temperature and use benzene or water as the solvent [31, 32].…”