To a stirred mixture of Cp2HfCl2 (269.5 mg, 0.710 mmol), AgOTf (365.5 mg, 1.423 mmol), and molecular sieves 4A (3 g) in dry CH2Cl2 (5 mL) was added a solution of mannobiose acceptor (541.1 mg, 0.593 mmol) and GlcNAc-donor (354.0 g, 0.609 mmol) in dry CH2Cl2 (10 mL) at −78° C. The mixture was stirred for 2 h and at −40° C. for 1 h. Insoluble materials were removed by passage through silica gel and the filtrate was then diluted with EtOAc, washed with brine, aq. NaHCO3 and brine successively, dried over Na2SO4, and evaporated in vacuo. The residue was purified by silica gel column chromatography (toluene:EtOAc, 15:1-10:1) to afford compound GlcNAc-mannobiose donor (393.4 mg, 45%).
