N-phenyl trifluoroacetimidates

Eventually, heptose trichloroacetimidate 129, activated by catalytic TMSOTf, proved to be superior for this glycosylation. The more reactive disaccharide N-phenyl trifluoroacetimidate 135 was then coupled with disaccharide 131 upon TMSOTf activation to give the desired a-linked tetrasaccharide 136 in a satisfactory yield of 72% (Scheme 2.29). 

---