Scheme 23.

Synthesis of phosphoramidite 134. Reaction conditions 1: (a) TBDMSCl, imidazole, pyridine, 33 h, 99%; (b) vinyl acetate, Pd(OAc)₂, PPh₃, Et₃N, DMF, 70 °C, 16 h, 68%; (c) OsO₄, 4-methylmorpholine-N-oxide, acetone H₂O t-BuOH (4:1:1), 15 h, 44%; (d) Ac₂O, pyridine, 44 h, 96%; (e) TBAF, THF, 14 h, 75%; (f) DMTrCl, DMAP, Et₃N, pyridine, 22 h, 78%; (g) [(iPr)₂N]₂POCH₂CH₂CN, tetrazole, 2.5 h, quant. Reaction conditions 2: (a) TBDMSCl, imidazole, DMF, over night; (b) 5 mol % Pd(MeCN)₂Cl₂, Bu₃SnCH=CH₂ (1.5 equiv), MeCN, 80 °C; (c) cat. OsO₄, NMO (2.5 equiv), acetone H₂O t-BuOH (4:1:1); (d) Ac₂O (4 equiv), pyridine; (e) TBAF (3 equiv), AcOH (2 equiv), THF; (f) DMTrCl (1.5 equiv), pyridine; (g) [(iPr)₂N]₂POCH₂CH₂CN (1.8 equiv), DCI (0.7 equiv), MeCN CH₂Cl₂ (1:10).