Silica supported boron triuoride nanoparticles; Dimedone; 2-naphthol; Aromatic aldehydes; Xanthenes. Ane cient and convenient synthesis of benzo [a] xanthene-11-one derivatives has been achieved by a one-pot, three-component reaction of various aromatic aldehydes with 2-naphthol and dimedone in the presence of Silica supported boron triuoride nanoparticles (BF3-SiO2 NPs) as a mild solid acid catalyst in improved yields.