Scheme 1. Construction of BC, EF and BCEF oligosaccharidesa.
a Conditions: (a) Tf2O, DTBMP, ADMB, CH2Cl2, −78 to 0 °C, 75%; (b) mCPBA, CH2Cl2, −78 to 0 °C, 70%; (c) Tf2O, DTBMP, ADMB, CH2Cl2, −42 °C, 84%; (d) Bu2BOTf, BH3·THF, THF, −60 °C, 83%; (e) Tf2O, DTBMP, ADMB, CH2Cl2, −60 °C, 50%. DTBMP = 2,6-di-tert-butyl-4-methylpyridine, ADMB = 4-allyl-1,2-dimethoxybenzene
