3.1.13. (3*S*,4*S*)-7-ethynyl-5,8-dihydroxy-4-methoxy-3-pentylisochroman-1-one (**8**)

To a solution of diMOM alkyne derivative **8a** (6.3 mg, 13.6 μmol) in MeOH (1.2 mL) was added 6 M aqueous HCl (0.40 mL) at room temperature. After stirring for 24 h at the same temperature, 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 column chromatography (EtOAc:*n*-hexane = 1:4 to 1:1) to give alkyne derivative **8** (3.3 mg, 67%) as a yellow solid. m.p. 132–133 ◦C; 1H-NMR (500 MHz, CDCl3) δ 11.20 (1H, s), 7.22 (1H, s), 6.03 (1H, br-s), 4.76 (1H, d, *J* = 2.5 Hz), 4.51 (1H, ddd, *J* = 2.5, 5.1, 8.2 Hz), 3.40 (3H, s), 3.39 (1H, s), 1.94 (1H, m), 1.84 (1H, m), 1.70–1.50 (1H, overlapped), 1.45 (1H, m), 1.40–1.25 (4H, overlapped), 0.91 (3H, t, *J* = 7.0 Hz); 13C-NMR (125 MHz, CDCl3) δ 168.6, 157.3, 145.1, 127.8, 123.4, 112.6, 108.0, 83.2, 81.4, 77.7, 69.7, 57.0, 31.5, 29.7, 24.8, 22.5, 14.0.; IR (KBr) 3294, 2956, 2930, 2859, 1679, 1434, 1172 cm−1; HRMS (ESI) *m*/*z* (M + H)<sup>+</sup> calculated for (C17H21O5) <sup>+</sup> 305.1389, found 305.1391.
