Glycosyl Thioimidates as Versatile Glycosyl Donors for Stereoselective O-Glycosylation and Convergent Oligosaccharide Synthesis

This review discusses the synthesis and application of glycosyl thioimidates as glycosyl donors in stereoselective glycosylation and convergent oligosaccharide assembly. Although a broad introduction and a thorough description of earlier studies of glycosyl thioimidates is presented, the main focus of this review is on S-benzoxazolyl (SBox) and S-thiazolinyl (STaz) derivatives developed by the authors. These novel thioimidates often provide higher stereoselectivity and yields in glycosylations in comparison to other existing approaches. The unique activation conditions of the SBox and STaz glycosides allowed the design of conceptually novel strategies for oligosaccharide synthesis. Such innovative approaches, as the inverse armed-disarmed strategy, the O-2/O-5 cooperative effect in glycosylation, the temporary deactivation concept, and orthogonal activation of the STaz vs. S-ethyl moieties are discussed.