Scheme 3.
Reagents and conditions: (a) 7a or 7b, EDCI, HOBt, i-Pr2NEt, CH2Cl2, 25 °C, 16 h, 80%; (b) LiOH.H2O, THF/MeOH/H2O (3:1:1), 25 °C, 16 h, 99%; (c) from 13a, LiAlH4, dry THF, reflux, 15 h, 88%; (d) MnO2, CH2Cl2, 25 °C, 5 h; (e) NaClO2, NaH2PO4, t-BuOH/H2O, 2-methyl-2-butene, 25 °C, 4 h, 45% (over 2 steps).