Novel ionic liquid [2-Eim] HSO₄as a dual catalytic-solvent system for preparation of hexahydroquinolines under green conditions

Abstract

A novel Brønsted acidic ionic liquid 2-ethyl imidazolium hydrogen sulfate, [2-Eim] HSO4, was synthesized. Its structure was investigated using FT-IR, 1 H NMR, 13 C NMR, UV, TGA and DTA spectra. This ionic liquid is utilized as a highly efficient and homogeneous catalyst for the promotion of hexahydroquinolines via one-pot multi-component condensation of aromatic aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate at room temperature and neat conditions. Also, optimization of the reaction conditions was investigated using the response surface method {Central Composite Design (CCD)}. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst could be reused and recovered at least four times without appreciable loss of activity.

Straightforward Hantzsch four‐ and three‐component condensation in the presence of triphenyl(propyl‐3‐sulfonyl)phosphoniumtrifluoromethanesulfonate {[TPPSP]OTf} as a reusable and green mild ionic liquid catalyst

“…[23] Significant rate and yield enhancements were also reported for Hantzsch reactions carried out under microwave irradiation. [24][25][26] The utilization of cyclic 1,3-diketone in the Hantzsch reaction for the synthesis of polyhydroquinoline and acridine has recently been demonstrated using nickel nanoparticles, [27] 1-vinyl-3-ethylimidazolium iodide as an IL catalyst, [28] amberlyst-15, [29] sulfonated organic heteropolyacid salts, [30] protic pyridinium IL OTf, [31] {[HMIM]C(NO 2 ) 3 }, [32] SnO 2 nanoparticles, [33] [Bsim]Cl, [34] [2-Eim]HSO 4 , [35] [pyridine-SO 3 H]Cl [36] and nano-ferrous ferric oxide (nano-Fe 3 O 4 ). [37] Following our attempts to develop a novel room temperature IL as a catalyst in synthetic methodologies, herein is reported a simple and green one-pot synthesis of polyhydroquinoline and acridine derivatives via Hantzsch four-and three-component condensation reactions in high yields using an acidic IL, triphenyl(propyl-3-sulfonyl)phosphoniumtrifluoromethanesulfonate, as a catalyst for the first time (1).…”

Ionic Liquid Solvation versus Catalysis: Computational Insight from a Multisubstituted Imidazole Synthesis in [Et2NH2][HSO4]

“…Brønsted‐acidic ILs are perfect agents for proton exchange (see Scheme ) in a nucleophilic addition reaction. [HSO 4 ] − may act as a proton donor and it has been hypothesized in a recent study that it may also act as a proton acceptor as the anionic component of 2‐ethyl imidazolium hydrogen sulfate . [HSO 4 ] − , as the acidic component of the IL, can donate a proton to the carbonyl‐containing species rather easily to become [SO 4 ] 2− , which may then accept a proton from a nucleophile (ammonia or benzyl amine in this study) and convert back to hydrosulfate.…”

“…[HSO 4 ] À may act as ap rotond onor and it has been hypothesized in ar ecent study that it may also act as ap roton acceptor as the anionic component of 2-ethyl imidazolium hydrogen sulfate. [22] [HSO 4 ] À ,a st he acidic component of the IL, can donate ap rotont ot he carbonyl-containing speciesr ather easily to become [SO 4 ] 2À ,which may then accept aproton from anucleophile (ammonia or benzyl amine in this study) and convert back to hydrosulfate. Strong acids, such as H 2 SO 4 ,are not capable of acting in the same way.I nt he H 2 SO 4 case, there is al ow concentration of protona cceptors in the medium to catalyze the reactiona sw ell as the IL.…”

First report of the application of simple molecular complexes as organo-catalysts for Knoevenagel condensation

“…Further hexahydroquinolines 50 synthetic protocol has been chosen to test the wider applicability of our molecular complex as efficient catalyst. 27 We have successfully obtained the desired product ( …”