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, C 18 H 17 NO 5 , 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.