In the isoquinoline ring system of the title mol-ecule, C(16)H(16)N(2)O(5), the N-heterocyclic ring is in a half-boat conformation. The dioxaaza-spiro ring is essentially planar [maximum deviation = 0.022 (1) Å] and forms a dihedral angle of 24.56 (4)° with the benzene ring.