Abstract
In the title compound, C(10)H(9)NO(5)S, the fused ring system and the planar (r.m.s. deviation = 0.0037 Å) methoxy-carbonyl-methyl side chain form a dihedral angle of 84.67 (10)°. The crystal structure is stabilized by inter-molecular C-H⋯O hydrogen bonds. A triclinic polymorph of the title compound is already known [Siddiqui et al. (2008 ▶). Acta Cryst. E64, o859].