Concise and scalable syntheses of aglycon and
glycosyl donors.
(a) Regioselective C–H functionalizations enabled scalable
preparation of the aglycon 21. (b) Synthesis of glycosyl
donors 23a–c. Reagents and conditions are as follows:
(i) NBS, MeCN, r.t.; i-PrI, NaH, DMF, 0 to 70 °C.
(ii) [Ir(cod)OMe]2, dtbpy, HBpin, hexane, 80 °C. (iii)
Pd(OAc)2, KF, PMHS, THF, H2O, r.t. (iv) [Pd(dppf)Cl2]·CH2Cl2, KOH, MTBE/H2O, 80 °C, then 40% NaOH (aq). (v) K2S2O8, AgNO3, MeCN/H2O, 50 °C.
(vi) Pd/C, H2, MeOH, r.t.; Tf2O, Et3N, CH2Cl2, −78 °C; potassium vinyltrifluoroborate,
[Pd(dppf)Cl2]·CH2Cl2, Et3N, n-PrOH, reflux. (vii) LiAlH4, THF, 50 °C. (viii) Ac2O, AcOH, H2SO4, r.t. (ix) DMAPA, THF, 20 °C. (x) CCl3CN,
DBU, 4 Å MS, CH2Cl2, r.t. (xi) N-Phenyltrifluoroacetimidoyl chloride, K2CO3, acetone, r.t.