(±)-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-dimethoxy­homophthalic anhydride with thio­phene-2-carbaldehyde in the presence of 4-(dimethyl­amino)pyridine (DMAP) as a basic catalyst. The thio­phene ring of the title mol­ecule 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 thio­phene ring with respect to the C—C bond linking it to the rest of the mol­ecule. The six-membered ring of the 3,4-dihydro­isochromanone 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-dihydro­isochromanone ring system makes dihedral angles of 75.0 (2) and 77.2 (5)° with the disordered thio­phene rings. Inter­molecular O—H⋯O and C—H⋯O hydrogen bonds, as well as C—H⋯π inter­actions, lead to the observed supra­molecular structure.