Glycosyl phosphates TMSOTf

Glycosyl phosphates as glycosyl donors were introduced by Hashimoto [469]. Their glycosylation reaction is promoted most frequently by TMSOTf [469]. Less common is the use of TDSOTf [277], BFa-EtjO [277], Znij [277], TfOH [277] or LiC104 [470] (Table 4.10). 

Treatment of active vinyl glycosides with NIS/TMSOTf in CH2CI2 in the presence of dibenzyl phosphate gives good yield of glycosyl phosphates [184]. 

The aromatic phenol was varied to explore the scope of the O-to-C conversion with mannosyl phosphates. Using phosphate 9, the a-C-mannosides of 2-naphthol and 3-benzyloxy phenol (23 and 25, Table 1) were synthesized in excellent yield. O-Mannosides were obtained exclusively with less nucleophilic aromatic systems, such as 3-acetoxy phenol. Several non-phenolic aromatic systems were unsuccessful in the formation of C-aryl or O-aryl glycosides. Reaction of 9 with furan, thiophene, trimethoxybenzene, and indole in the presence of TMSOTf did not result in any product formation. Interestingly, activation of 9 in the absence of any aromatic nucleophiles gave 26 as the major product via an intramolecular C-glycosylation (Figure 1) (79). 

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