Scheme 9.

Synthesis of Common Key Building Block 78^a

^aReagents and conditions. a) NaBH₄ (2.0 equiv), CeCl₃·7H₂O (1.3 equiv), MeOH, −20→0 °C, 3 h, 99%; b) Ac₂O (2.0 equiv), Et₃N (3.0 equiv), 4-DMAP (0.2 equiv), CH₂Cl₂, 0 °C, 1 h, 91%; c) Pd(OAc)₂ (0.02 equiv), PPh₃ (0.1 equiv), Et₃N (1.2 equiv), PhMe, 25→110 °C, 3 h, 86%; d) O₂, TPP (0.0036 equiv), CH₂Cl₂, 25°C, 24 h, 73%; e) thiourea (2.0 equiv), MeOH, 25 °C, 2 h, 84%; f) TIPSOTf (1.1 equiv), Et₃N (2.0 equiv), CH₂Cl₂, 0 °C, 30 min, 96%; g) (im)₂C=S (1.2 equiv), PhMe, 110 °C, 3 h, 90%; h) P(OMe)₃, 111 °C, 12 h, 82%; i) HCl aq. (1.0 M), CH₂Cl₂/Et₂O (1:1), 0 °C, 10 min, 98%.