title: Revisit of the phenol O-glycosylation with glycosyl imidates, BF₃·OEt₂ is a better catalyst than TMSOTf.
abstract: With BF(3)·OEt(2) as the catalyst, the glycosylation of phenols with glycosyl trichloroacetimidates (or N-phenyl trifluoroacetimidates) bearing 2-O-participating groups leads to the desired 1,2-trans-O-glycosides in generally excellent yields without formation of the 1,2-cis-anomers. However, with TMSOTf as the catalyst, the outcomes of the corresponding phenol O-glycosylation are highly dependent on the nucleophilicity of the phenols; less nucleophilic is the phenol, higher amounts of the 1,2-cis-O-glycoside together with more side-products are generated. 1,2-Orthoesters have been found to be the major products at a low temperature (<-70 °C) in all these phenol O-glycosylation reactions, which are transformed into the final products at a higher temperature. BF(3)·OEt(2) is an effective catalyst to promote the conversion of 1,2-orthoesters into the corresponding 1,2-trans-O-glycosides. However, the 1,2-orthoesters could be converted into the dioxolenium triflate and glycosyl triflate in the presence of TMSOTf, these intermediates which might be in equilibrium with the glycosyl oxocarbenium related species lead to the final mixture of the α/β-O-glycosides and side-products.
authors.affiliation: State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.
authors.forename: Yali
authors.initials: Y
authors.lastname: Li
authors.forename: Huaping
authors.initials: H
authors.lastname: Mo
authors.forename: Gaoyan
authors.initials: G
authors.lastname: Lian
authors.forename: Biao
authors.initials: B
authors.lastname: Yu
mesh_terms: D001880:Boranes / Q000737:chemistry*; D002384:Catalysis; D006027:Glycosides / Q000737:chemistry; D006031:Glycosylation; D007096:Imidoesters / Q000737:chemistry*; D008698:Mesylates / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
chemical_list: D001880:Boranes; D006027:Glycosides; D007096:Imidoesters; D008698:Mesylates; D010636:Phenols; D014297:Trimethylsilyl Compounds; C053353:trimethylsilyl trifluoromethanesulfonate; C101707:boron trifluoride etherate; D010100:Oxygen