Crystal structure of 3-meth­oxy­carbonyl-2-(4-meth­oxy­phen­yl)-8-oxo-1-aza­spiro[4.5]deca-1,6,9-trien-1-ium-1-olate

The title compound, C₁₈H₁₇NO₅, was prepared by a synthetic strategy based on the Heck reaction from Morita–Baylis–Hillman adducts. The five-membered ring adopts a slightly twisted conformation on the C_a—C_m (a = aromatic and m = methyl­ene) bond. The dihedral angle between the five-membered ring and the spiro aromatic ring is 89.35 (7)°; that between the five-membered ring and the 4-meth­oxy­benzene ring is 4.65 (7)°. Two short intra­molecular C—H...O contacts occur. In the crystal, mol­ecules are linked by C—H...O hydrogen bonds to generate a three-dimensional network.