Reagents and Conditions. a) CBr4, triphenylphosphine, triethylamine, 81%; b) Diethylmethylphosphite, 110 °C, 95%; c) TBAF, THF, 91%, d) Triphenylphosphine, 2,6-dichloropurine, diisopropyl azodicarboxylate, an. THF, 75%; e) 2 M NH3 in i-PrOH, 70 °C, 60%; f) Iodotrimethylsilane, an. CH2Cl2, 20% combined yield.