Journal
TETRAHEDRON
Volume 71, Issue 21, Pages 3385-3395Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2015.03.092
Keywords
Nitrogen heterocycles; Pyrazoles; Alkynes; Tandem cyclisation; Fluorescence
Categories
Funding
- Research Council of Lithuania [MIP-076/2012]
- Republic of Lithuania
- European Social Fund
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The synthesis of 2H- and 3H-pyrazolo[4',3':3,4]pyrido[1,2-a]benzimidazole derivatives from 3-alkynyl- or 5-alkynylpyrazole-4-carbaldehydes and benzene-1,2-diamines was carried out using copper-free tandem cyclisation. When 2,3-diaminopyridine was used as the diamine component in this type of tandem cyclisation, 3H-pyrazolo[4,3-c]imidazo[1,2-a:5,4-b']dipyridine derivatives were obtained. Copper catalysis and microwave activation were required for the reaction of 5-alkynylpyrazole-4-carbaldehydes and 1,8-naphthalenediamine, affording the corresponding 13,13a-dihydro-3H-pyrazolo[4',3':3,4]pyrido [1,2-a]perimidines. The structure assignments were based on data from H-1, C-13 and N-15 spectroscopy and single-crystal X-ray diffraction analyses. The optical properties of the obtained new heterocyclic derivatives were studied by UV-vis and fluorescence spectroscopy. (C) 2015 Elsevier Ltd. All rights reserved.
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