Aluminium lithium hydride → tert-butyl 2-(hydroxymethyl)-4-((tetrahydro-2H-pyran-2-yl)oxy)piperidine-1-carboxylate

To a solution of the product of step E (5.0 g, 14.6 mmol) in tetrahydrofuran (50 mL) at −20° C. was added lithium aluminum hydride (1.14 g, 30 mmol). After stirring at −20° C. for 1 h, the reaction was quenched by slow addition of water (10 mL). The resulting suspension was filtered through Celite and the filtrate concentrated in vacuo to dryness. Water (60 mL) was added and the aqueous phase was extracted with ethyl acetate (3×30 mL). The combined organic extracts were dried over anhydrous Na2SO4, filtered, and concentrated in vacuo. Purification by flash column chromatography (SiO2, 4:1 to 7:3, hexanes/ethyl acetate) afforded tert-butyl 2-(hydroxymethyl)-4-((tetrahydro-2H-pyran-2-yl)oxy)piperidine-1-carboxylate (4.1 g, 81%) as a colorless oil: 1H NMR (CDCl3, 400 MHz) δ 4.73-4.63 (m, 1H), 4.44-4.23 (m, 1H), 4.02-4.00 (m, 1H), 3.90-3.70 (m, 4H), 3.50-3.48 (m, 1H), 3.21-2.42 (m, 1H), 2.09-1.93 (m, 1H), 1.82-1.71 (m, 5H), 1.54 (br s, 5H), 1.47 (s, 9H).