Use of Protecting Groups for Chemoselective Glycosylations

FIGURE 4.3 Correlation of the calculated TS energies from inner strain caused by the two fused rings and the experimental results. Source Satoh et al. [70]. Reproduced with permission of American Chemical Society. 

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

Ley and coworkers also showed that the degree of arming/disarming is a continuum and proposed that identification of donors with several different levels of reactivity would make it possible to prepare rather complex oligosaccharides by a one-pot procedure without the need for intermediate purifications. Subsequently, Chi-Huey Wong and coworkers reported a comprehensive study determining relative reactivities of 

SCHEME 4.19 Competition experiment showing the super-arming effect of a participating group at C2 in trans orientation with respect to the leaving group. Box, benzoxazolyl DMTST, dime thy l(methy lthio )sulfonium trifl ate. 

SCHEME 4.20 Super-arming by steric effect, (a) Influence of conformation on the reactivity of glycosides, (b) Conformational change induced by bulky silyl ethers. 

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