To a solution of 3,4-dimethoxy-6-(4-pyridyl)hydroxymethylbenzaldehyde dimethyl acetal (18.4 g) in a mixture of acetic acid (50 ml) and toluene (50 ml) is added maleic acid dimethyl ester (8.64 ml), and the mixture is refluxed for one hour. To the mixture is added methanesulfonic acid (9.33 ml), and the mixture is refluxed for 8 hours while the generated water is removed by using a Dean-stark apparatus. The mixture is cooled to room temperature and concentrated. The residue is dissolved in chloroform, and the pH value thereof is adjusted to pH 8 with an aqueous potassium carbonate solution. The mixture is extracted with chloroform, and the extract is washed, dried, concentrated, and the residue is crystallized from ether to give 1-(4-pyridyl)-2,3-bis(methoxycarbonyl)-6,7-dimethoxynaphthalene (13.5 g).
