Cascade embedding triethyltryptophanium iodide ionic liquid (TrpEt3+I-) on silicated titanomagnetite core (Fe3-xTixO4-SiO2@TrpEt3+I-): A novel nano organic-inorganic hybrid to prepare a library of 4-substituted quinoline-2-carboxylates and 4,6-disubstituted quinoline-2-carboxylates

A library of substituted quinolone-2-carboxylates (4,6-disubstituted quinolone-2-carboxylates, 6-substituted quinoline dialkyl-2,4-dicarboxylates, and 6-substituted 4-[2-methoxy-2-oxoethyl]quinoline-2-methylcarboxylates) was obtained through different scopes of one-pot and one-step MCRs such as (a) three-component reaction of aromatic amines, dialkyl acetylenedicarboxylates, and terminal alkenes/ketones; (b) pseudo three-component reaction of anilines and dialkyl acetylenedicarboxylates; and (c) pseudo three-component reaction of anilines and methyl propiolate under solvent-free conditions at 100 degrees C. The promoter of these annulation processes is a novel inorganic-organic core-shell that was obtained from silicated titanomagnetite, tryptophan amino acid, and ethyl iodide. The tryptophan embedded on the silicated titanomagnetite core (Fe3-xTixO4-SiO2) followed by alkylation with ethyl iodide subsequently result in in situ preparation of triethyltryptophanium iodide ionic liquid (TrpEt(3)(+)I(-)). The final nanohybrid (Fe3-xTixO4-SiO2@TrpEt(3)(+)I(-)) was characterized by field-emission scanning electron microscope, EDAX, FT-IR, TGA/DTG, vibrating sample magnetometer, and X-ray fluorescence techniques. The highlighted features of the protocol are as follows: (a) synthesis of a vast range of substituted quinolines through a straightforward method from simple substrates under solvent-free conditions, (b) utilizing various scopes of functionalities as substrates, (c) simple separation of the nano promoter via an external magnet, (d) regioselectivity in the cascade annulation procedure, and (e) recovery and reusability of the nanocomposite within three runs without significant activity loss.

Automated summary

This study synthesized a series of substituted quinolines using simple substrates through a straightforward method under solvent-free conditions, with the use of various functional substrates. The newly developed inorganic-organic core-shell catalyst can be easily separated and recycled with the help of an external magnet, demonstrating high selectivity and reusability in the cascade annulation process.