A Highly Efficient and Fast Method for the Synthesis of Biscoumarins Using Tetrabutylammonium Hexatungstate [TBA]₂[W₆O₁₉] as Green and Reusable Heterogeneous Catalyst

Abstract

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 6 O 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.

A Rapid, Efficient and Green Method for Synthesis of 3,3'-Arylmethylene-bis-4-hydroxycoumarins without Use of any Solvent, Catalyst or Solid Surface

“…It is the hemorrhagic agent responsible for the sweet clover disease of cattle and has also been employed for the prevention and treatment of thrombosis 12 . 3,3'-Arylmethylene-bis-4-hydroxycoumarins (3) are usually synthesized by condensing 4-hydroxycoumarin (1) with various aldehydes (aromatic, heterocyclic and α,β-unsaturated) (2) using different catalysts and media [8][9][10][13][14][15][16][17][18][19] . Some of these methods require long reaction time, use of expensive catalysts and organic solvents and tedious work up 8,10 .…”

“…Some of these methods require long reaction time, use of expensive catalysts and organic solvents and tedious work up 8,10 . The current literature shows that there has been a growing trend towards green synthesis of these compounds [13][14][15][16][17][18][19] . However, in such reported green methods use of catalysts, solid surfaces, solvents etc.…”

Oxidation Reactions Catalyzed by Polyoxomolybdate Salts

“…For example, the Keggin-type POM anion [PW 12 O 40 ] 3− can be used as catalyst for esterification [21] and for epoxidation reactions in ionic liquids [22]. The compound [(n-C 4 H 9 ) 4 N] 2 [W 6 O 19 ] was found to be a catalyst for the synthesis of biscoumarins, which was investigated by Davoodna [23]. From these results it appears that tungsten-based WCC-POMs can exhibit excellent catalytic performance because of controllable redox and acidic properties [24 -26], which make them economical and environmentally acceptable.…”

A Convenient, Eco-friendly, and Efficient Method for Synthesis of 3,3'-Arylmethylene-bis-4-hydroxycoumarins "On-water"

“…16 3,3'-Arylmethylene-bis-4-hydroxycoumarins (3), commonly known as biscoumarins, are usually synthesized by condensing 4-hydroxycoumarin (1) with various aldehydes (aromatic, heterocyclic, and α,β-unsaturated) 2 using different catalysts and media. [13][14][15][17][18][19][20][21][22][23][24] Some of these methods require long reaction time, use of expensive catalysts and organic solvents and tedious work up. 13,15,24 In four recent papers, the said condensation has been reported to be performed in water by employing molecular iodine, 17 ruthenium(III) chloride hydrate 24 or surfactants like TBAB 18 or DDS 19 as catalyst.…”