Reagents and conditions:
(a)
BnBr, NaH, DMF, 0 °C–room temperature, 2 h. (b) 80% aqueous
HOAc, reflux, 1 h. (c) Bu2SnO, BnBr, Bu4NBr,
MeCN, 3 Å molecular sieves, reflux, 24 h. (d) Bu4NHSO4, BnBr, DCM: 5% aqueous NaOH (1:1), room temperature. (e)
Ac2O, pyr, room temperature, 12 h. (f) Compound 16, NIS, TMSOTf, dioxane:toluene (3:1 v/v), 3 Å molecular sieves,
room temperature, 30 min. (g) 90% TFA, room temperature, 15 min. (h)
Ac2O, pyr, room temperature, 3 h. (i) 6-Chloropurine, BSA,
TMSOTf, MeCN, 70 °C, overnight. (j) NH3, EtOH, 70
°C, 5 days. (k) (1) (BnO)2PN(iPr)2, ImOTf,
DCM, room temperature, 30 min; (2) mCPBA, −78 °C–room
temperature, 1 h. (l) Cyclohexene, Pd(OH)2, MeOH, H2O, 80 °C, overnight.