• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4286-4290
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• 2011

A novel catalytic synthesis of biscoumarins from 4-hydroxycoumarin and aromatic aldehydes has been developed. The reaction occurs in ethanol in the presence of tetrabutylammonium hexatungstate $[TBA]_2[W_6O_{19}]$ as catalyst to give the corresponding products in high yields. This new approach has short reaction times, clean reaction profiles, and simple experimental and workup procedures. Moreover, the catalyst can be easily recovered by filtration and used at least three times with only slight reduction in its catalytic activity.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1508-1512
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• 2013

A simple and efficient synthesis of 2,4,5-trisubstituted imidazoles was achieved via a one-pot three-component cyclocondensation of benzil, aromatic aldehydes, and ammonium acetate in the presence of a catalytic amount of tetrabutylammonium hexatungstate $[TBA]_2[W_6O_{19}]$ as a heterogeneous catalyst under thermal solvent-free conditions. The key features of this methodology are operational simplicity, high yields, short reaction times, and a recyclable catalyst with a very easy work up.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3289-3294
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• 2013

An efficient method for the preparation of 8-benzylidene-4-phenyl-3,4,5,6,7,8-hexahydro-1H-quinazolin-2-ones/thiones from the reaction of aromatic aldehydes with cyclohexanone and urea or thiourea in the presence of Tetrabutylammonium hexatungstate, $[TBA]_2[W_6O_{19}]$, as an efficient, inexpensive catalyst under thermal and solvent-free conditions has been developed. Good yields, short reaction times, straightforward workup, reusability of the catalyst, and green conditions are the most obvious advantages of this procedure.