Glycosylation armed-disarmed

The concept of armed/disarmed glycosyl donors was subsequently extended by other groups to thioglycosides21 and selenoglycosides.64 A similar strategy has been used by Friesen and Danishefsky to achieve chemoselectivity in electrophilic addition to glycal double bonds.65... 

Scheme 12.22. Synthesis of heptasaccharide 147 using the armed-disarmed glycosylation approach, byjona and co-workers [75],...

SCHEME 4.18 Selective glycosylation using the armed-disarmed glycosylation strategy. Cbz, benzyloxycarbonyl. 

Ley and coworkers reported the one-pot synthesis of tetrasaccharide 176 by combining selective activation with reactivity-based armed-disarmed glycosylation [113]. As shown in Scheme 6.35, the first chemoselective coupling was achieved via selective activation of the fluoride donor 173 over the selenoglycoside acceptor 174. The resulting disaccharide intermediate was more armed than the bifunctional... 

SCHEME 4.29 Oligosaccharide synthesis by armed-disarmed glycosylations. 

SCHEME 5.17 Armed-disarmed glycosylation based on the electron withdrawing/donating properties of substituents. 

In the traditional approaches of oligosaccharide synthesis, the product of a glycosylation reaction had to be isolated and it required some chemical transformation(s) to make it suitable for the next glycosylation reaction. In some of the synthetic strategies described in Section 5.4, such as in the sequential glycosylations and in the armed-disarmed glycosylations, the product of one... 

An additional factor which was used to tune reactivity in armed-disarmed glycosylations is the dependency of glycosylation rates on the solvent [92]. Thus, one-pot glycosylations were accomplished by performing the first glycosylation in ether, which slows down the reaction, and performing the second glycosylation in dichloromethane [92]. 

Scheme 6 Oligosaccharide synthesis based on armed-disarmed glycosylation.

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