A new chalcone of the coumarin, C(21)H(18)O(7), containing an annulated α-pyrone ring, was obtained by condensation of the borate complex of ac-yl(hydr-oxy)coumarin with trimethoxy-benzaldehyde. The structure exhibits intra-molecular hydrogen bonding between the hydroxyl oxygen and the ketonic oxygen in the coumarin group. The bicyclic coumarin fragment and the benzene ring form a dihedral angle of 17.1 (4)°. The crystal packing involves dimers inter-connected by C-H⋯O hydrogen bonding.