A solution of dimethyl sulfoxide (202 mg) in methylene chloride (1.0 ml) was added dropwise to a solution of oxalyl dichloride (247 mg) in methylene chloride (10 ml) over 5 minutes at -78° C. After 10 minutes, a solution of (2R)-1-[3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl)acryloyl]-2-(2-hydroxyethyl)piperidine (trans isomer) (364 mg) in methylene chloride (3.4 mg) was added dropwise over 10 minutes at -78° C. The solution was stirred at -78° C. for 20 minutes and at -45° C. for 1 hour. Triethylamine (986 μl) was added to the solution and the mixture was stirred at -20°~0° C. for 20 minutes. Saturated ammonium chloride solution (20 ml) was added to the reaction mixture was the mixture was extracted with methylene chloride (10 ml×2). The combined extracts were washed with brine (10 ml), dried over magnesium sulfate and evaporated in vacuo. The crude material was purified by column chromatography on silica gel (10 g) with a mixture of methylene chloride and ethyl acetate (10:1) as an eluent to give (2R)-1-[3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl)acryloyl]-2-(formylmethyl)piperidine (trans isomer) (139.0 mg) as an oil.
