Tris(hydrogensulfato) boron as a solid heterogeneous catalyst for the rapid synthesis of α,α′-benzylidene bis(4-hydroxycoumarin) derivatives

α,α′-Benzylidene bis(4-hydroxycoumarin) derivatives were readily prepared in a few minutes with good yields through the reaction of an aromatic aldehyde and 4-hydroxycoumarin in aqueous media in the presence of catalytic tris(hydrogensulfato) boron [B(HSO4)3].