BORONIC ACID CATALYZED REGIO- AND 1,2-cis-STEREOSELECTIVE GLYCOSYLATION OF UNPROTECTED SUGAR ACCEPTORS VIA S_nI-TYPE MECHANISM

摘要

1,2-cis-Glycosides are frequently found in various biologically active natural products and glycoconjugates. Therefore, to explore the precise roles of these glycosides, efficient syntheses of these 1,2-cis-glycosides have been paid considerable attention. Based on the background, complex oligosaccharides and glycoconjugates possessing 1,2-cis-glycosides have been synthesized in a highly stereoselective manner. However, these synthetic schemes were highly dependent on protecting group strategies to control the regio- and stereoselectivities of each glycosylation step, leading to a decrease in step and atom economies of the overall process. Therefore, regio- and 1,2-cis-stereoselective chemical glycosylation without any protecting groups have been highly desirable. In this context, we have recently developed regio- and 1,2-cis-stereoselective glycosylations using diol sugar acceptor-derived boronic esters [1], Herein we wish report a novel regio- and 1,2-cis-stereoselective glycosylations of 1,2-anhydro donors and unprotected sugar acceptors using boronic acid catalyst.