Glycosylation TMSOTf

In fact, other studies have shown that TMSOTf catalyzes the glycosylation of a silylated acceptor with a silylated hemiacetal donor [49]. Nudel man s procedure was applied to the synthesis [1-glucuronide 30, isolated in 57% yield. Kiyoi and Kondo have applied the TMSOTf activation protocol to protected L-fucose hemiacetal donors for glycopeptide synthesis and obtained glycopeptide fragment 31 in 74% yield (a p, 20 1) [50], Posner and Bull have developed a procedure that uses excess TMSOTf in the presence of molecular sieves (SYLOSIV A4) to synthesize various l.l -linked disaccharides such as the galactopyranose dimer 32 [51,52]. 

Simple alkyl carbonates have also been used as glycosyl donors with the addition of an external glycosyl acceptor. Sinay and coworkers have reported that 2-propenyl carbonate donors, such as 151 (R = 2-propenyl), are activated with TMSOTf at —25 °C to afford good yields of disaccharide products [358]. Disaccharide... 

Although the existence of glycosyl triflates has only been demonstrated for the triflic anhydride and benzenesulfenyl triflate promoter systems, presumably the same intermediates may be invoked on preactivation with other triflate-incorporat-ing systems such as TMSOTf (Scheme 4.42) [332] and triflic add (Scheme 4.43) [84,333]. 

Reaction of glycosyl thioimidate 79 with aa -dibromo-m-xylene in the presence of NaH as a base and 15-crown-5 as a supporting reagent allowed the intermediate 80 (Scheme 4.88). Treatment of the diol 81 with dibutyltin oxide in dry toluene and then reaction with 80 in the presence of tetrabutylammonium iodide afforded the desired O-linked intermediate 82. Activation of this compound with NIS-TMSOTf afforded 83 in a good yield. Hydrogenolysis followed by acetylation gave the desired disac-... 

As an example, glycosylation of trichloroacetimidate 10 with acceptor 11 using catalytic amounts of TMSOTf in DCM at —78 °C gave disaccharide 12 in 89% yield and good a-stereoselectivity (Scheme 5). 

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