Osmium tetroxide (2.5 wt. % in t-BuOH; 0.3 mL, 0.001 mmol) was added to a solution of benzyl 4-[1-(ethoxycarbonyl)-3-methylbut-3-en-1-yl]piperidine-1-carboxylate (2.88 g, 8.01 mmol) in tetrahydrofuran (30 mL). Sodium periodate (5.14 g, 24.0 mmol) in water (26 mL) was added to the reaction mixture. After 5 days, the reaction was diluted with saturated aqueous sodium sulfite and saturated aqueous sodium bicarbonate and extracted with ethyl acetate (3×). The combined organic washes were dried over sodium sulfate, filtered and concentrated to give the title compound. MS 362.2 (M+1).
