3.1.20. (3*S*,4*S*)-7-(azidomethyl)-5,8-dihydroxy-4-methoxy-3-pentylisochroman-1-one (**13**)

To a solution of diMOM azide derivative **13a** (8.3 mg, 19.6 μmol) in MeOH (1.5 mL) was added 6 M aqueous HCl (0.49 mL) at room temperature. After stirring for 4 h at 40 ◦C, the reaction was quenched by adding saturated aqueous NaHCO3 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 = 3:7) to give nitro derivative **13** (3.1 mg, 49%) as a white solid. m.p. 98–99 ◦C; 1H-NMR (400 MHz, CDCl3) δ 10.98 (1H, s), 7.10 (1H, s), 5.81 (1H, br-s), 4.78 (1H, d, *J* = 2.9 Hz), 4.52 (1H, ddd, *J* = 2.9, 5.4, 8.5 Hz), 4.45 (1H, d, *J* = 14.4 Hz), 4.42 (1H, d, *J* = 14.4 Hz), 3.41 (3H, s), 1.93 (1H, m), 1.86 (1H, m), 1.70-1.50 (1H, overlapped), 1.47 (1H, m), 1.40–1.25 (4H, overlapped), 0.91 (3H, t, *J* = 7.1 Hz); 13C-NMR (125 MHz, CDCl3) δ 169.1, 154.4, 145.7, 126.2, 124.6, 121.8, 108.0, 81.7, 70.4, 57.2, 49.3, 31.9, 30.0, 25.2, 22.8, 14.3.; IR (KBr) 2959, 2924, 2857, 2108, 1654, 1441, 1293, 1170 cm<sup>−</sup>1; HRMS (ESI) *m*/*z* (M + H)<sup>+</sup> calculated for (C16H22N3O5) <sup>+</sup> 336.1559, found 336.1563.
