title: Cation Clock Reactions for the Determination of Relative Reaction Kinetics in Glycosylation Reactions: Applications to Gluco- and Mannopyranosyl Sulfoxide and Trichloroacetimidate Type Donors.
abstract: The development of a cation clock method based on the intramolecular Sakurai reaction for probing the concentration dependence of the nucleophile in glycosylation reactions is described. The method is developed for the sulfoxide and trichloroacetimidate glycosylation protocols. The method reveals that O-glycosylation reactions have stronger concentration dependencies than C-glycosylation reactions consistent with a more associative, S(N)2-like character. For the 4,6-O-benzylidene-directed mannosylation reaction a significant difference in concentration dependence is found for the formation of the β- and α-anomers, suggesting a difference in mechanism and a rationale for the optimization of selectivity regardless of the type of donor employed. In the mannose series the cyclization reaction employed as clock results in the formation of cis and trans-fused oxabicyclo[4,4,0]decanes as products with the latter being strongly indicative of the involvement of a conformationally mobile transient glycosyl oxocarbenium ion. With identical protecting group arrays cyclization in the glucopyranose series is more rapid than in the mannopyranose manifold. The potential application of related clock reactions in other carbenium ion-based branches of organic synthesis is considered.
authors.affiliation: †Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States.
authors.forename: Philip O
authors.initials: PO
authors.lastname: Adero
authors.affiliation: †Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Furukawa
authors.affiliation: ‡Institut de Chimie des Substances Naturelles, CNRS-ICSN UPR2301, Université Paris-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
authors.forename: Min
authors.initials: M
authors.lastname: Huang
authors.affiliation: †Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States.
authors.forename: Debaraj
authors.initials: D
authors.lastname: Mukherjee
authors.affiliation: ‡Institut de Chimie des Substances Naturelles, CNRS-ICSN UPR2301, Université Paris-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Retailleau
authors.affiliation: ‡Institut de Chimie des Substances Naturelles, CNRS-ICSN UPR2301, Université Paris-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
authors.forename: Luis
authors.initials: L
authors.lastname: Bohé
authors.affiliation: †Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States.
authors.forename: David
authors.initials: D
authors.lastname: Crich
mesh_terms: D000081:Acetamides / Q000737:chemistry*; D001597:Benzylidene Compounds / Q000737:chemistry; D001671:Biochemistry / Q000379:methods*; D060326:Chemistry Techniques, Synthetic; D062845:Chloroacetates / Q000737:chemistry*; D003500:Cyclization; D005936:Glucans / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry; D006031:Glycosylation; D008358:Mannose / Q000737:chemistry*; D013454:Sulfoxides / Q000737:chemistry*
chemical_list: D000081:Acetamides; D001597:Benzylidene Compounds; D062845:Chloroacetates; D005936:Glucans; D006027:Glycosides; D013454:Sulfoxides; C009528:trichloroacetamide; D008358:Mannose