Reagents and conditions: (a)652 (1) 350.3a, CH3SO3H (15 mol %), (2) DDQ (3 equiv), DCM, 0 °C, 2 h, then
rt 15 min; (b) (1) 350.3b, p-TsOH·H2O (1 equiv), (2) DDQ (6 equiv), DCM, 0 °C, 2 h, then
rt 15 min; (c) (1) H2SO4, TFA, rt, 5 days, (2)
Zn(OAc)2·2H2O (60 equiv), CHCl3/MeOH, 50 °C, o/n; (d) (1) H2SO4, TFA,
0 °C, 30 min, (2) Zn(OAc)2·2H2O (60
equiv), CHCl3/MeOH, 50 °C, o/n; (e) DDQ (8 equiv),
Sc(OTf)3 (8 equiv), toluene, 100 °C, 5 h; (f) DDQ
(8 equiv), Sc(OTf)3 (8 equiv), toluene, 80 °C, 4 h;
(g) H2SO4, TFA, 0 °C, 30 min, (2) Zn(OAc)2·2H2O (40 equiv), CHCl3/MeOH, 50
°C, o/n; (h) DDQ (5 equiv), Sc(OTf)3 (5 equiv), toluene,
rt, 3 h; (i) DDQ (12 equiv), Sc(OTf)3 (12 equiv), toluene,
80 °C, 3 h.