Reaction Steps
To a solution of acid chloride prepared from 20a (30 mg, 0.067 mmol) in toluene was added dropwise a solution of N-hydroxythiopyridone 22 (11 mg, 0.09 mmol) and DMAP (2 mg) in toluene (0.5 mL) and pyridine (0.3 mL) at room temperature under N2 in the dark. After stirring for 10 min, t-butylmercaptane (0.5 mL) was added and the mixture was irradiated with white light (tungsten lamp, 100 W) at room temperature. After stirring for 10 min, N2 was introduced to the mixture under a slightly reduced pressure to remove residual t-butylmercaptane for 30 min. Usual workup and purification by silica gel preparative TLC [developed with hexane-Et2O (1:)] afforded 21 (18.5 mg, 68%) as an oil, [α]22D +36.8° (c 1.85, CHCl3); 1H NMR (CDCl3) δ2.000-2.150 (2 H, m, H-2ax, H-2eq), 2.010 (6 H, s, acetyl), 2.082 (3 H, s, acetyl), 2.119 (3 H, s, acetyl), 2.137 (3 H, s, acetyl), 3.882 (1 H, dd, J5,4 =1.5, J5,6 =10.0 Hz, H-5), 4.115 (1 H, dd, J7',6 =4.5, J7',7 =12.5 H, H-7'), 4.437 (1 H, dd, J7,6 =2.5, J7,7' =12.5 Hz, H-7), 5.073 (1 H, ddd, J3,4 =3.0, J3,2eq =5.0, J3,2ax =12.5 Hz, H-3), 5.165 (1 H, ddd, J6,7 =2.5, J6,7' =4.5, J6,5 =10.0 Hz, H-6), 5.303 (1 H, dd, J4,5 =1.5, J4,3 =3.0 Hz, H-4), 5.748 (1 H, dd, J1,2eq =3.0, J1,2ax =10.0 Hz, H-1); 13C NMR (CDCl3) δ20.59, 20.59, 20.65, 20.65, 20.84, 30.35, 62.26, 63.84, 67.32, 67.90, 71.62, 91.67, 168.60, 169.60, 169.83, 170.30, 170.54. HRMS (M+Cs+) calcd C17H24O11Cs 537.0373, found 537.0359.
