6-(tert-butyldimethylsilyloxy)-2-naphthaldehyde (4.0 g, 14 mmol), AcOH (1.8 g, 28 mmol) and methyl azetidine-3-carboxylate (3.2 g, 28 mmol, 2.0 equiv) in DCE (30 mL) were stirred at 85° C. for 1 h. Then NaBH3CN (1.8 g, 28 mmol, 2.0 equiv) was added to the mixture at 50° C. and stirred for 2 h at 85° C. The reaction mixture was quenched with water, extracted with DCM and washed with brine, dried over Na2SO4 and concentrated to obtain crude product. The crude product was purified by silica gel chromatography (DCM:MeOH=40:1) to give the title compound (2.7 g, 50%) as a yellow oil. ESI-MS (M+1)+: 386.2. 1H NMR (400 MHz, CDCl3) δ: 7.72-7.68 (m, 3H), 7.37-7.34 (m, 1H), 7.15-7.10 (m, 2H), 3.94 (s, 2H), 3.81-3.76 (m, 4H), 3.74 (s, 3H), 3.50-3.44 (m, 1H), 1.02 (s, 9H), 0.25 (s, 6H).
