To a pre-cooled (0° C.) solution of 29 (609 mg, 0.569 mmol) in anhydrous DCM (2.8 mL, 0.2 M) was added trichloroacetonitrile (114 μL, 1.138 mmol, 2 eq). A solution of DBU (4.3 μL, 0.05 eq, 0.0285 mmol) in anhydrous DCM (0.3 mL) was added. The mixture was stirred at 0° C. for 4 h and TLC (hexane-EtOAc=65:35) indicated complete conversion. The crude mixture was evaporated onto silica gel and purified by silica column chromatography (2.5×14 cm, gradient elution with hexane-EtOAc-Et3N 210:20:0.5, 200:50:0.5, 180:60:0.5, 150:70:0.5). The product fractions were combined, evaporated and dried in a vacuum desiccator over P2O5 o/n to give the trichloroacetimidate 30 as white foam (530 mg, 77%), used without further purification in the next step.
