A solution of N-methoxymethanamine hydrochloride (1.48 g) in toluene (15 mL) was cooled to 0° C., and trimethylaluminum (1.4M hexane solution, 10.9 mL) was added dropwise. The reaction mixture was stirred at room temperature for 1.5 hr, and a solution of ethyl 2-[5-(methylsulfanyl)pyridin-2-yl]-3-(tetrahydro-2H-pyran-4-yl)propanoate (1.57 g) in toluene (15 mL) was added dropwise. The reaction mixture was stirred at room temperature for 6 hr, saturated aqueous sodium hydrogen carbonate and saturated aqueous Rochelle salt solution were added and the mixture was stirred for 1 hr. The reaction mixture was extracted with ethyl acetate, and the ethyl acetate layer was washed with saturated brine, dried (MgSO4) and concentrated. The residue was subjected to silica gel column chromatography, and the title compound (404 mg, yield 25%) was obtained as a pale-yellow amorphous solid from a fraction eluted with ethyl acetate-hexane (9:1, volume ratio).
