Multicomponent Reaction of Pyridinium Salts,
β
‐Nitrostyrenes and Ammonium Acetate under the DBU/Acetic Acid System: Access to 2,4,6‐Triarylpyridine Derivatives
A survey of the literature reveals that the number of coumarin derivatives having heterocyclic moieties either as substituent groups or fused with parent coumarin nucleus possesses a variety of functions and are widely used in drugs and dyes. Because of this wide utility, the synthesis of coumarin has remained a subject of active interest. Looking at the importance of these heterocoumarins and with a view to exploring new methods of their synthesis, the present work was undertaken and this synthesis deals with various 2-aryl-pyrido [3,2-c] coumarins. The compounds have been synthesized by reacting Mannich bases of various 4-hydroxy coumarins with pyridinium salts of various aroyl methyl bromides in the presence of ammonium acetate and acetic acid. All the compounds synthesized have been characterized by analytical and spectral data.
Keywords: Pyrido, Coumarins, Krohanke’s reaction.
Some new imidazolyl pyrazole derivatives have been synthesized using benzil, ammonium acetate, and heterocyclic aldehyde in ethanol and acetic acid under ultra sound irradiation. The obtained products using this approach are having high purity and good in yield. By conducting the reactions in ethanol, the solid products were precipitated out and could be isolated simply by filtration. The synthesized compounds were characterized by various analytical techniques such as 1H and 13C NMR and further supported by mass spectroscopy.
Acetic acid mediated regioselective synthesis of novel 2,4,5-trisubstituted thiazole derivatives has been reported by a domino reaction of thiosemicarbazide and aldehydes/ketones/isatin, to generate thiosemicarbazones (in situ) followed by addition of arylglyoxal and active methylene/activated C–H acids/pyrazole/indole in ethanol at 80 °C.
Reactions of N-pyridinium phenancylides with different a, β-unsaturated ketones give 2,4,6-triarylsubstituted pyridines, 2,6-diphenyl-4-(2-pyridyl) pyridines, 2-benzylidene-4,6-diphenyl pyridines and 2,4,6-triphenyl-3-bromopyridine. Ammonium acetate in acetic acid was used as cyclization agent. The structure of the products are supported by IR and NMR spectra.
Enaminones react with a variety of active methyl and methylene reagents in presence of ammonium acetate to yield functionally substituted pyridines in good yields. The reaction proceeded via initial Michael addition across the double bond followed by cyclization. The reaction of enaminone with aromatic aldehyde in acetic acid/ammonium acetate afforded the dihydropyridine that was oxidized to the corresponding pyridine.
The title compound, C27H27N3O2S, was obtained via a multicomponent reaction using benzaldehyde, ethyl acetoacetate, ammonium acetate and phenyl isothiocyanate. The pyrimidine ring assumes a half-boat conformation. The crystal packing is stabilized by N—H...O and N—H...S hydrogen bonds. The phenyl group of the anilinocarbonothioyl group displays some rotational disorder.
Synthesis and characterization of some novel coumarin based various 2-aryl-pyrido [3,2-c] coumarins