Engaging a thiazole-DMAD zwitterion in novel one-pot multicomponent reactions involving chromones. Expeditious synthesis of thiazolo- and chromenothiazolopyridines

Dipolar cycloaddition strategy for three-component synthesis of chromeno[3',4':3,4]pyrido[2,1-a]isoquinoline derivatives

A rapid and efficient protocol to fused pentacyclic compounds, the chromeno[3',4':3,4]pyrido[2,1-a]isoquinolines, via a diastereoselective 1,4-dipolar cycloaddition reaction of isoquinoline, dialkyl acetylenedicarboxylates, and 3-acetyl coumarins, is described.

New Hybrid Hydrazinyl Thiazole Substituted Chromones: As Potential α-Amylase Inhibitors and Radical (DPPH & ABTS) Scavengers

Current research is based on the identification of novel inhibitors of α-amylase enzyme. For that purpose, new hybrid molecules of hydrazinyl thiazole substituted chromones 5-27 were synthesized by multi-step reaction and fully characterized by various spectroscopic techniques such as EI-MS, HREI-MS, 1H-NMR and 13C-NMR. Stereochemistry of the iminic bond was confirmed by NOESY analysis of a representative molecule. All compounds 5-27 along with their intervening intermediates 1-4, were screened for in vitro α-amylase inhibitory, DPPH and ABTS radical scavenging activities. All compounds showed good inhibition potential in the range of IC50 = 2.186-3.405 µM as compared to standard acarbose having IC50 value of 1.9 ± 0.07 µM. It is worth mentioning that compounds were also demonstrated good DPPH (IC50 = 0.09-2.233 µM) and ABTS (IC50 = 0.584-3.738 µM) radical scavenging activities as compared to standard ascorbic acid having IC50 = 0.33 ± 0.18 µM for DPPH and IC50 = 0.53 ± 0.3 µM for ABTS radical scavenging activities. In addition to that cytotoxicity of the compounds were checked on NIH-3T3 mouse fibroblast cell line and found to be non-toxic. In silico studies were performed to rationalize the binding mode of compounds (ligands) with the active site of α-amylase enzyme.

Computational study on the mechanism of the three-component reaction of dimethylacetylene dicarboxylate and triphenylphosphine with 2-acetylbutyrolactone

The molecular mechanism of the three-component reaction of triphenylphosphine, dialkyl acetylene dicarboxylate, and 2-acetylbutyrolactone to synthesize the stabilized phosphorus ylide and 1,3-butadiene derivative via the intramolecular Wittig reaction has been investigated using the density functional theory method at the B3LYP/6-31G level of theory. Two possible reaction pathways have been characterized in detail to form the cyclobutene intermediate and in the next step; the cyclobutene intermediate undergoes the conrotatory ring-opening reaction to produce the 1,3-butadiene derivative along two possible pathways. The calculated results indicate that two pathways (pathways II and II-a) are the most energy favorable among all of the pathways, so they occur more than do the others. Moreover, the phosphorus ylide is more stable than the corresponding 1,3-butadiene, demonstrating that the intramolecular Wittig reaction could not easily occur at room temperature, which is in agreement with the experimental results.

Synthesis of benzimidazole[2.1-b][1,3]oxazine spirooxindoles via three-component reaction of N-benzylbenzimidazole, acetylenedicarboxylates, and N-alkylisatins

The three-component reaction of N-benzylbenzimidazole, dialkyl acetylenedicarboxylate, and N-alkylisatins in tetrahydrofuran at room temperature afforded the novel functionalized benzimidazole[2.1-b][1,3]oxazine spirooxindoles in good yields. (1)H NMR spectra indicated that two diastereoisomers with a ratio of 1:3-1:6 exist in the obtained spirooxindole derivatives.

One-pot synthesis of chromenylfurandicarboxylates and cyclopenta[b]chromenedicarboxylates involving zwitterionic intermediates. A DFT investigation on the regioselectivity of the reaction

The reaction of 1:1 zwitterionic intermediates generated in situ from either tert-butylisocyanide or cyclohexylisocyanide and acetylenedicarboxylates with 3-formylchromones is described, whereupon either chromenylfurandicarboxylates or cyclopenta[b]chromenedicarboxylates are formed, depending on the nature of the chromone 6-position substituent and also on the acetylene ester group. In addition, from the reaction with a 1:2 zwitterionic intermediate, cyclohepta[b]chromenetetracarboxylates are isolated. The regioselectivity of the reaction was also investigated by DFT calculations. The geometries of the reactants, intermediate zwitterions, transition structures, and intermediate products, leading to the final products, were optimized using the B3LYP functional with the 6-31G(d) basis set. The structures of the products were elucidated by 1D and 2D NMR experiments. Full assignment of all (1)H and (13)C NMR chemical shifts has been achieved. Plausible mechanistic schemes are provided.