Double condensation of 3-coumaranone with aromatic carbonyl compounds catalyzed by Brønsted hyperacids under microwaves.

The acidic condensation of 3-coumaranone (benzofuran-2(3H)-one ) with aromatic carbonyl compounds (aldehydes, diones) conduct to different products depending of the acidity of the catalyst.

With poorly Bronsted acid such as acidic clay (K10, KSF), aurons (3- benzylidenebenzofuran-2(3H)-one and (or) 3-(hydroxyl(phenyl) methyl)benzofuran-2(3H)-on were formed according the microwave activation.

We reported herein that double condensation of 3-coumaranone with aromatic carbonyl compounds (aldehydes or polyones) take place with Brønsted hyperacids. The condensation under microwave irradiation of 3-coumaranone and 8-hydroxy-3- coumaranone with benzaldehydes or polyones (ninhydrin, isatin, phenanthraquinone, acenaphthoquinone) were studied in dimethylsulfoxide with pentafluoroanilinium triflate (PFAT) or without solvent with triflic acid as catalyst.

The 3,3’-(phenylmethylene)bis(benzofuran-2(3H)-ones were identified by HPLC coupled with mass spectroscopy and by NMR and then separated by preparative thin layer chromatography.

A reaction mechanism for this double condensation of 3-coumaranone with aromatic carbonyl compounds is proposed involving the addition of a carbocation to an enolic form of 3-coumaranone. This proposed mechanism is very close to the known reaction mechanism for the condensation of aldehyde with two molecules of 4- hydroxycoumarone to form dicoumarols in presence of acidic catalysts.

Aurones are known for their numerous biological properties, it is likely that these 3,3’- (phenylmethylene)bis(benzofuran-2(3H)-ones have interesting biological properties which will be studied in the near future.