A mixture of 5.00 g of 5,6,7,7a-tetrahydro-4H-thieno[3,2-c]pyridin-2-one.p-toluenesulfonate, 2.47 g of tert-butyldimethylchlorosilane, 1.66 g of triethylamine and 15 ml of methylene chloride was stirred at room temperature (20° C.) for 3 hours. The produced 2-(tert-butyldimethylsilyloxy)-4,5,6,7-tetrahydrothieno[3,2-c]pyridine-p-toluenesulfonate was not isolated, 5.90 g of 2-chloro-α-methoxycarbonylbenzyl bromide and 3.02 g of triethylamine were added thereto, and the mixture was allowed to react.
