N. Ahmed, J. E. van Lier / Tetrahedron Letters 48 (2007) 5407–5409
5409
affect their reactivity or product yield. The assigned
structures of the products were established from their
spectral properties ( H and C NMR, and MS) and also
by comparison with available literature data (Table 1).
10. (a) Legeay, J. C.; Eynde, J. J. V.; Bazureau, J. P.
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13
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1
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G.; Reddy, G. S. K. K.; Reddy, C. S.; Yadav, J. S. Synlett
In conclusion, we have shown an efficient TaBr -cata-
5
lyzed one-pot synthesis of 3,4-dihydropyrimidin-2-
(
1H)-ones and thione analogs (4) by multicomponent
Biginelli reactions under solvent-free conditions, using
commercially available substrates and tantalum salt.
The advantages of this procedure over earlier reported
processes include its simplicity, fast and clean reactions,
high yield, and the absence of organic solvent.
2
003, 858–860; (g) Ma, Y.; Qian, C.; Wang, L.; Yang, M.
J. Org. Chem. 2000, 65, 3864–3868; (h) Suzuki, I.;
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Acknowledgment
7
861–7864; (i) Adib, M.; Ghanbary, K.; Mostofi, M.;
Ganjali, M. R. Molecules 2006, 11, 649–654; (j) Bose, D.
S.; Fatima, L.; Mereyala, H. B. J. Org. Chem. 2003, 68,
This work was supported by the Canadian Institutes of
Health Research (CIHR, grant MOP- 44065).
5
1
87–590; (k) De, S. K.; Gibbs, R. A. Synthesis 2005, 1748–
750; (l) Reddy, C. V.; Mahesh, M.; Raju, P. V. K.; Babu,
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5
3
6
4
5
14. General Procedure for the Biginelli reaction: TaBr (5–
2
10 mol %) was added to a stirred mixture of aldehydes
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5
to complete dissolution of TaBr . The solvent was
gradually evaporated by heating and the neat reaction
mixture was heated with stirring for 40–45 min at 70–
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monitoring showed that the reaction was completed after
45 min. After cooling the solid precipitate was filtered and
washed with cold water and ethanol under reduced
pressure and the residue was crystallized from ethanol or
ethyl acetate–hexane (1:3) to afford the pure product (4).
5
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