Scheme 5:

Reagents and conditions: (a) 2-azidoethanol, NIS, TfOH, MS 4Å, CH₂Cl₂-ether (1:4), −20 °C, 30 mins, then 0 °C, 1 h, 62%; (b) NIS, TMSOTf, MS 4Å, CH₂Cl₂, −20 °C, 30 min, 76%; (c) CH₃ONa, CH₃OH, r t, 2 h, 92%; (d) NIS, AgOTf, 4Å MS, CH₂Cl₂, −20 °C, 45 min, 71%; (e) (i) CH₃ONa, CH₃OH, r t, 2 h; (ii) BnBr, NaH, DMF, r t, 2 h; (iii) 80% AcOH, 80 °C, 2 h; (iv) Ac₂O, pyridine, r t, 3 h; (v) 20% Pd(OH)₂-C, H₂, CH₃OH, rt, 24 h, overall yield 47%.