An efficient synthesis of thiopyrano[5,6-c]coumarin/[6,5-c]chromones through intramolecular domino Knoevenagel hetero Diels–Alder reactions

Magnetically recoverable silica catalysed solvent-free domino Knoevenagel-hetero-Diels-Alder reaction to access divergent chromenones

A three-component domino Knoevenagel-hetero-Diels-Alder (DKHDA) reaction between 1,3-dicarbonyl, aldehydes/ketones, and alkenes/alkynes leading to the divergent synthesis of chromenones, dihydrochromenones, and spirocyclic chromenones is reported. The reaction was carried out under solvent-free conditions using a magnetically separable silica (Fe3O4@SiO2) catalyst. While two component DKHDA reactions are known, this is the first example of a three component DKHDA reaction involving 1,3-dicarbonyl, ketones, and alkynes producing spirocyclic pyranone derivatives. Twenty-six different highly substituted chromenones were synthesized using this methodology. A wide substrate scope due to the multicomponent nature of the reaction, high atom economy, the use of inexpensive and non-toxic recyclable silica as the catalyst, and solvent free reaction conditions make it an advantageous process. The catalyst was characterized using different analytical techniques such as XRD, IR, HRTEM, VSM, and TGA. Based on the earlier reports a mechanism has also been proposed.

A domino synthetic approach for new, angular pyrazol- and isoxazol-heterocycles using [DBU][Ac] as an effective reaction medium

Some new, angular pyrazol- and isoxazol-heterocycles have been synthesized by the reaction of pyrazolone/isoxazolone with typical ketone-based substrates—O-alkenyloxy/alkynyloxy-acetophenones.

Graphene oxide nanosheets: a highly efficient and reusable carbocatalyst catalyzes the Michael-cyclization reactions of 4-hydroxycoumarins, 4-hydroxypyrone and 4-hydroxy-1-methylquinolinone with chalcone derivatives in aqueous media

Graphene oxide nanosheets: a highly efficient and reusable carbocatalyst catalyzes the Michael-cyclization reactions of 4-hydroxycoumarins, 4-hydroxypyrone and 4-hydroxy-1-methylquinolinone with chalcone derivatives in aqueous media.

Molecular structure and spectroscopic studies on novel complexes of coumarin-3-carboxylic acid with Ni(II), Co(II), Zn(II) and Mn(II) ions based on density functional theory

Novel Ni(II), Co(II), Zn(II) and Mn(II) complexes of coumarin-3-carboxylic acid (HCCA) were studied at experimental and theoretical levels. The complexes were characterised by elemental analyses, FT-IR, (1)H NMR, (13)C NMR and UV-Vis spectroscopy and by magnetic susceptibility measurements. The binding modes of the ligand and the spin states of the metal complexes were established by means of molecular modelling of the complexes studied and calculation of their IR, NMR and absorption spectra at DFT(TDDFT)/B3LYP level. The experimental and calculated data verified high spin Ni(II), Co(II) and Mn(II) complexes and a bidentate binding through the carboxylic oxygen atoms (CCA2). The model calculations predicted pseudo octahedral trans-[M(CCA2)(2)(H(2)O)(2)] structures for the Zn(II), Ni(II) and Co(II) complexes and a binuclear [Mn(2)(CCA2)(4)(H(2)O)(2)] structure. Experimental and calculated (1)H, (13)C NMR, IR and UV-Vis data were used to distinguish the two possible bidentate binding modes (CCA1 and CCA2) as well as mononuclear and binuclear structures of the metal complexes.

A facile iodine(III)-mediated synthesis of 3-(3-aryl-1-phenyl-1H-pyrazol-4-yl)-[1,2,4]triazolo[4,3-a]pyridines via oxidation of 2-((3-aryl-1-phenyl-1H-pyrazol-4-yl)methylene)-1-(pyridin-2-yl)hydrazines and their antimicrobial evaluations

BACKGROUND

Fused heterocyclic 1,2,4-triazoles have acquired much importance because of their interesting biological properties. Although a number of methods have been reported in the literature which includes oxidation with phosphorus oxychloride, lead tetraacetate, bromine, etc., hypervalent iodine reagents have emerged as reagents of choice for various synthetically useful transformations due to their low toxicity, ready availability and ease of handling.

RESULTS

A series of new 3-(3-aryl-1-phenyl-1H-pyrazol-4-yl)-[1,2,4]triazolo[4,3-a]pyridines 4 has been conveniently synthesized by oxidative cyclization of 2-(3-aryl-1-phenyl-1H-pyrazol-4-yl)methylene)-1-(pyridin-2-yl)hydrazines 3 promoted with iodobenzene diacetate under mild conditions (up to 90% isolated yields). All the new compounds were tested in vitro for their antimicrobial activity.

CONCLUSIONS

Iodine(III)-mediated oxidative approach has offered an easy access to new 3-(3-aryl-1-phenyl-1H-pyrazol-4-yl)-[1,2,4]triazolo[4,3-a]pyridines 4. The antibacterial and antifungal activities of newly synthesized compounds have proved them potent antimicrobial agents.

Revised Structure by Computational Methods for a Coumarin Isolated from Zanthoxylum Rhoifolium (Rutaceae)

On the basis of theoretical methods using DFT/B3LYP/6-31G* geometries and HF/6-311+G** GIAO NMR predictions, the 13C NMR spectroscopic data of a coumarin from Zanthoxylum rhoifolium was reassigned. The structure was revised to be 4-methoxy-3-(3-methylbut-2-enyl)-2 H-chromen-2-one (4) and not 3-methoxy-4-(3-methylbut-2-enyl)-2 H-chromen-2-one (2), as assumed previously.