Cp2HfCl2/AgOTf

In another report of polymer-supported synthesis of an oligosaccharide Cp2HfCl2-AgOTf was used for activation of glycosyl fluoride on a resin (Fig. 6) [12a]. 

Reaction of 2-fluoroglycosyl fluoride 148 with 6-bromo-2-naphthol with Cp2HfCl2-AgOTf catalysis affords the fused carbohydrate-containing tetracycles 149 and 150 in 44% and 21% yields respectively. Similar chemistry was applied to phenol derivatives. ... 

Scheme 5. Polymer-supported synthesis of trimannoside on the basis of the orthogonal strategy. Reagents and conditions (a) DMTST in CH2CI2, room temp., (b) Cp2HfCl2-AgOTf in CH2CI2, 0 °C — room temp., (c) (i) NaOMe (ii) H2-Pd(OH)2 in MeOH-EtOAc. Yields were calculated on a weight basis.

This strategy has been further extended to polymer-supported glycoside synthesis [lib], A diglycosyl fluoride attached to a PEG polymer is connected to a disaccharide by use of Cp2HfCl2 and AgOTf (Fig. 5). 

Treatment of 67 with Cp2HfCl2 and AgOTf has been found to give the regio-selective intramolecular glycosidation product 68 in 37% yield (Scheme 21) [40], This regioselectivity was in agreement with Monte Carlo calculations. 

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