Scheme 18.^a.

^a Reagents and conditions: (a) SOCl₂, MeOH; (b) HCl·NH₂OH, MeOH, AcONa; (c) t-BuOCl, CH₂Cl₂; (d) CH₂Cl₂, 0 °C, 12 h; (e) Al-Hg, H₂O/MeCN; (f) p-O₂NPhSO₂Cl, MeCN, NEt₃; (g) TBSCl, DBU; (h) NBS, H₂O/acetone; (i) MeCN, K₂CO₃, 60 °C, then 208; (j) 20 mol% SnCl₄, CH₂Cl₂; (k) Ac₂O, K₂CO₃; (l) HSCH₂CO₂H, LiOH, DMF; (m) Boc₂O, MeCN; (n) RuCl₃, NaIO₄, H₂O; (o) DBU, PhH, 70 °C; (p) HCO₂H, THF, 60 °C; (q) LiAlH₄, THF.