0.5 ml of Triethylamine was added to a solution of 200 mg of 2,6-dimethyl-5-(3-methyl-2-butenyloxycarbonyl)-4-(3,4,5-trimethoxyphenyl)-dihydropyrimidine in 5 ml of tetrahydrofuran (THF) and 2-heptyl chloroformate dissolved in 6 ml of THF was added dropwise. The 2-heptyl chloroformate was prepared by adding 0.25 ml of N,N-diethylaniline dissolved in 2 ml of THF to a solution of 0.15 g of 2-heptyn-1-ol and 0.1 mg of trichloromethyl chloroformate in 4 ml of THF in a separate reaction vessel. After stirring at room temperature for 1 hr, the reaction mixture was concentrated under reduced pressure. The residue was purified on silica gel by column chromatography (silica gel 20 g, eluant:benzene/ethyl acetate 9:1) to obtain 187 mg (69% yield) of title product.
