Amberlyst 15-catalyzed Glycosylation Reaction

2,3-Unsaturated glycosides are useful chiral intermediates in the synthesis of biologically active compounds, such as glycopeptide building blocks and oligosaccharides. They have also been employed to synthesize many important antibiotics and nucleosides. Lewis acid-catalyzed allylic rearrangement of glycal is well utilized as Ferrier reaction and widely employed to produce 2,3-unsaturated glycosides. Various strong Lewis acid catalysts, such as BF₃·Et₂O or SnCl₄ are generally required. Other oxidants, such as DDQ,CAN and I₂, are also known to promote the Ferrier rearrangement under different conditions. However, many of these procedures have drawbacks in terms of utilizations,stereoselectivities,yields and toxic or costly catalysts.Glycosyl trichloroacetimidate donors have been widely adopted in complex carbohydrate construction. Traditionally, the glycosyl imidate-based glycosylations are activated by strong and moisture sensitive Lewis acids, including BF₃·Et₂O,TMSOTf and several moisture-stable solid promoters, such as HClO₄/silica and AW 300 MS. Many of these methods suffer from disadvantages such as inconvenience to handle,significant cooling and strictly anhydrous conditions,large excess or high cost of catalyst.Amberlyst 15, a strong acidic ion exchange resin, is widely used in organic synthesis. This thesis has developed Amberlyst 15-catalyzed Ferrier glycosidation of glycal and disarmed glycosyl trichloroacetimidate-based glycosylations. A series of O- or S-linked oligosaccharides and glycosylated amino acids, including structurally diverse 2,3-unsaturated-O- and 5-glycosides have been synthesized with high stereoselectivity under mild conditions in moderate to excellent yields(50-98%). Compared with the existing techniques, this activation method is intentionally optimized to fulfill the requirements for a more practical glycosylation process, such as the mild conditions, the convenience to handle and environmentally benign procedure.