To a solution of tert-butyl propiolate (3.54 ml, 25.81 mmole) in tetrahydrofuran (60 ml) was added at -70° C. under the argon atmosphere a solution of 2.0M lithium diisopropylamide in a heptane-tetrahydrofuran-ethylbenzene mixture (13.0 ml, 26 mmole), and the mixture was stirred for 30 minutes. The reaction mixture was then added to a solution of 4-methoxycarbonyl-2-nitrobenzaldehyde (4.5 g, 21.5 mmole) in tetrahydrofuran (100 ml), and the mixture was further stirred at -75° C. for 5 minutes. After a solution of acetic acid (3.2 ml, 53.3 mmole) in tetrahydrofuran (10 ml) and water were added, the reaction mixture was extracted with ethyl acetate (400 ml). The organic layer was washed with dilute hydrochloric acid, a saturated aqueous sodium hydrogen carbonate solution and a saturated aqueous saline in this sequence. After the organic layer was dried over anhydrous magnesium sulfate, the solvent was removed under reduced pressure to give the crude product of tert-butyl 4-hydroxy-4-(4-methoxycarbonyl-6-nitrophenyl)-2-butynoate as a brown oil (7.655 g).
