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Khai Ching Tan

Bio: Khai Ching Tan is an academic researcher from Monash University Malaysia Campus. The author has contributed to research in topics: Tautomer & One-pot synthesis. The author has an hindex of 2, co-authored 2 publications receiving 11 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, it was found that 3-amino-substituted 5-aminopyrazoles can be effectively prepared via hydrolytic decarboxylation of the corresponding 3-5-diaminopyrazole-4-carboxylates under microwave irradiation.

8 citations

Journal ArticleDOI
TL;DR: In this paper, 3-Amino-substituted 5-aminopyrazoles were found to be suitable substrates for the synthesis of new 4-AMR[1,5-a][1,3,5]triazines (5-aza-9deaza-adenines) when used in the one-pot, three-component reaction with cyanamide and triethyl orthoformate under microwave irradiation.

7 citations


Cited by
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Journal ArticleDOI
TL;DR: A revision of data is provided on the present subject, based on investigations using theoretical and experimental methods, together with the applications of the compounds in synthesis, to contribute to a deeper understanding of structure/reactivity relationships in this class of heterocycles.
Abstract: Pyrazoles are known as versatile scaffolds in organic synthesis and medicinal chemistry, often used as starting materials for the preparation of more complex heterocyclic systems with relevance in the pharmaceutical field. Pyrazoles are also interesting compounds from a structural viewpoint, mainly because they exhibit tautomerism. This phenomenon may influence their reactivity, with possible impact on the synthetic strategies where pyrazoles take part, as well as on the biological activities of targets bearing a pyrazole moiety, since a change in structure translates into changes in properties. Investigations of the structure of pyrazoles that unravel the tautomeric and conformational preferences are therefore of upmost relevance. 3(5)-Aminopyrazoles are largely explored as precursors in the synthesis of condensed heterocyclic systems, namely pyrazolo[1,5-a]pyrimidines. However, the information available in the literature concerning the structure and chemistry of 3(5)-aminopyrazoles is scarce and disperse. We provide a revision of data on the present subject, based on investigations using theoretical and experimental methods, together with the applications of the compounds in synthesis. It is expected that the combined information will contribute to a deeper understanding of structure/reactivity relationships in this class of heterocycles, with a positive impact in the design of synthetic methods, where they take part.

31 citations

Journal ArticleDOI
TL;DR: These factors, pyrazole aromaticity and intra- and inter-molecular interactions, seem to have a considerable influence on the choice of tautomer.
Abstract: A series of disubstituted 1H-pyrazoles with methyl (1), amino (2), and nitro (3) groups, as well as ester (a) or amide (b) groups in positions 3 and 5 was synthesized, and annular tautomerism was investigated using X-ray, theoretical calculations, NMR, and FT-IR methods. The X-ray experiment in the crystal state showed for the compounds with methyl (1a, 1b) and amino (2b) groups the tautomer with ester or amide groups at position 3 (tautomer 3), but for those with a nitro group (3b, 4), tautomer 5. Similar results were obtained in solution by NMR NOE experiments in CDCl3, DMSO-d6, and CD3OD solvents. However, tautomer equilibrium was observed for 2b in DMSO. The FT-IR spectra in chloroform and acetonitrile showed equilibria, which can be ascribed to conformational changes of the cis/trans arrangement of the ester/amide group and pyrazole ring. Theoretical analysis using the M06-2X/6-311++G(d,p) method (in vacuo, chloroform, acetonitrile, and water) and measurement of aromaticity (NICS) showed dependence on internal hydrogen bonds, the influence of the environment, and the effect of the substituent. These factors, pyrazole aromaticity and intra- and inter-molecular interactions, seem to have a considerable influence on the choice of tautomer.

11 citations

Journal ArticleDOI
TL;DR: In this article, it was found that 3-amino-substituted 5-aminopyrazoles can be effectively prepared via hydrolytic decarboxylation of the corresponding 3-5-diaminopyrazole-4-carboxylates under microwave irradiation.

8 citations

Journal ArticleDOI
TL;DR: In this paper, 3-Amino-substituted 5-aminopyrazoles were found to be suitable substrates for the synthesis of new 4-AMR[1,5-a][1,3,5]triazines (5-aza-9deaza-adenines) when used in the one-pot, three-component reaction with cyanamide and triethyl orthoformate under microwave irradiation.

7 citations

Journal ArticleDOI
TL;DR: In this article, a one-pot method for the preparation of N2,6-diaryl-5, 6-dihydro-1,3,5-triazine-2,4-diamines was developed using a three-component synthesis of 1,6,Diaryl, 1, 6,Dihydroid- 1, 3, 5,5,triazine, 2, 4 diamines followed by their Dimroth rearrangement.
Abstract: A convenient one-pot method for the preparation of N2,6-diaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines was developed using a three-component synthesis of 1,6-diaryl-1,6-dihydro-1,3,5-triazine-2,4-diamines followed by their Dimroth rearrangement to the desired products. The prepared compounds crystallized from ethanol as ethanol clathrates (1 : 1). X-ray crystallography on several products confirmed the adoption of 5,6-dihydro-tautomer. The thermal analysis and powder X-ray diffraction experiments on selected compounds suggested that thermal desolvation of crystals was irreversible.

6 citations