Study On The 3-Cr Methodology Of New Thiochromeno[2,3-b]Pyridine Scaffolds

Multicomponent reactions are the most enabling synthetic tools to enhance the efficiency. Following the main line of green chemistry and the principle of"atom economy", a new molecular framework of thiochromeno[2,3-b]pyridines has been constructed via three-component reactions by usingβ-(2-haloaroyl)thioacetanilides as polyfunctional synthons in the paper.In the first chapter, thioamides as versatile synthetic intermediates were reviewed firstly. Then the environmentally benign methods by using multicomponent reactions (MCRs), microwave-assisted combinatorial synthesis (MACS) and solid catalysts were summarized.In the second chapter, twenty-one new thiochromeno[2,3-b]pyridines were synthesized by the three components"one-pot"reaction ofβ-(2-chloroaroyl)- thioacetanilides, Meldrum's acid and aromatic aldehydes catalyzed by triethylamine firstly. In this reaction, seven different active sites were involved, two C-C bonds, one C-S bond, one C-N bond and two new rings (pyridine and thiopyran) were constructed with all reactants efficiently utilized via a sequence of Knoevenagel condensation, Michael addition, cyclization and intramolecular nucleophilic substitution reactions.In the third chapter, the eco-friendly KF/neutral Al2O3 and PEG6000 were combined as a catalyst. The reaction consisting ofβ-(2-haloaroyl)thioacetanilides, aldehydes and malononitrile has been demonstrated in the presence of KF/neutral Al2O3/ PEG6000 under microwave irradiation, leading to the first synthesis of the other thirty-one new thiochromeno[2,3-b]pyridines. At the same time, the mechanism of the catalyst was studied associating the characterization, and the success of this particular reaction may be attributed to the synergistic effect between KF/neutral Al2O3/PEG6000. Finally, the catalyst was reused through further treatment.Fifty-two compounds were synthesized, and the structures of all the synthesized compounds were characterized by IR, 1H NMR, 13C NMR and elemental analysis, some of them were further confirmed by MS spectrum. Four single-crystals were cultured and the structure of the unknown compounds could be confirmed conveniently by X-ray single-crystal diffraction analysis.