3.1.16. (3*S*,4*S*)-7-(hydroxymethyl)-4-methoxy-5,8-bis(methoxymethoxy)-3-pentylisochroman-1 one (**11a**)

To a solution of diMOM aldehyde derivative **12a** (20.0 mg, 50.5 μmol) in MeOH (0.25 mL) was added NaBH4 (2.1 mg, 55.5 μmol) at 0 ◦C. After stirring for 15 min at the same temperature, the reaction was quenched by adding water at 0 ◦C. The mixture was extracted with EtOAc (×3) and the combined organic layers were washed with brine, dried over Na2SO4, filtered, and concentrated under reduced pressure. The residue was purified with PTLC (EtOAc:*n*-hexane = 1:1) to give diMOM hydroxymethyl derivative **11a** (18.6 mg, 93%) as a white wax. 1H-NMR (400 MHz, CDCl3) δ 7.46 (1H, s), 5.25 (1H, d, *J* = 6.8 Hz), 5.24 (1H, d, *J* = 6.8 Hz), 5.15 (2H, s), 4.72 (1H, dd, *J* = 6.4, 12.5 Hz), 4.62 (1H, d, *J* = 1.2 Hz), 4.58 (1H, dd, *J* = 7.8, 12.5 Hz), 4.25 (1H, ddd, *J* = 1.2, 5.8, 8.0 Hz), 3.64 (3H, s), 3.55 (1H, t, *J* = 6.8 Hz), 3.50 (3H, s), 3.31 (3H, s), 2.05 (1H, m), 1.83 (1H, m), 1.65-1.50 (1H, overlapped), 1.43 (1H, m), 1.42–1.30 (4H, overlapped), 0.91 (3H, t, *J* = 6.8 Hz); 13C-NMR (125 MHz, CDCl3) δ 162.4, 152.7, 150.7, 138.7, 128.9, 120.8, 119.3, 102.2, 95.4, 81.2, 68.4, 61.4, 57.8, 57.2, 56.8, 31.9, 30.9, 25.2, 22.9, 14.4.; IR (KBr) 3443, 2957, 2928, 2859, 2828, 1724, 1153, 1012 cm<sup>−</sup>1; HRMS (ESI) *m*/*z* (M + H)<sup>+</sup> calculated for (C20H31O8)+ 399.2019, found 399.2017.
