(±)-trans-6,7-Dimeth­oxy-1-oxo-3-(2-thien­yl)isochroman-4-carboxylic acid

The title compound, C(16)H(14)O(6)S, was synthesized by the reaction of 6,7-dimethoxy-homophthalic anhydride with thio-phene-2-carbaldehyde in the presence of 4-(dimethyl-amino)pyridine (DMAP) as a basic catalyst. The thio-phene ring of the title mol-ecule is disordered over two sites with occupancies of 0.877 (3) and 0.123 (3). The disorder corresponds to an approximate 180° rotation of the thio-phene ring with respect to the C-C bond linking it to the rest of the mol-ecule. The six-membered ring of the 3,4-dihydro-isochromanone ring system is not planar [puckering parameters Q(T) = 0.571 (2) Å, θ = 115.2 (2)° and ϕ = 99.1 (2)°]. The benzene ring of the 3,4-dihydro-isochromanone ring system makes dihedral angles of 75.0 (2) and 77.2 (5)° with the disordered thio-phene rings. Inter-molecular O-H⋯O and C-H⋯O hydrogen bonds, as well as C-H⋯π inter-actions, lead to the observed supra-molecular structure.