title: Further studies on cation clock reactions in glycosylation: observation of a configuration specific intramolecular sulfenyl transfer and isolation and characterization of a tricyclic acetal.
abstract: The use of the 2-O-(2-trimethylsilylmethallyl) group as intramolecular nucleophile and cation clock reaction in the glucopyranose series depends on the nature of the glycosyl donor. As previously reported, with trichloroacetimidates the anticipated intramolecular Sakurai reaction proceeds efficiently and is an effective clock, whereas with sulfoxides complications arise. The source of these complications is now shown to be an intramolecular sulfenyl transfer reaction between the tethered allylsilane and the activated sulfoxide. These results illustrate how a different unimolecular clock reaction may be required for a given cation when it is generated from different donors in order to avoid side reactions. The synthesis and cyclization of a 2-O-(3-hydroxypropyl) glucopyranosyl sulfoxide leading on activation to the formation of a trans-fused acetal is also described. The formation of this crystallographically-established trans-fused acetal is discussed in terms of the high effective concentration of the intramolecular nucleophile which leads to a high degree of a SN2 character in the displacement of the α-glucosyl triflate or at the level of the corresponding α-CIP. The possible use of such intramolecular alcohols as clock reactions and their limitations is discussed.
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, MI 48202, USA.
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: Pascal
authors.initials: P
authors.lastname: Retailleau
authors.affiliation: Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI 48202, USA. Electronic address: dcrich@chem.wayne.edu.
authors.forename: David
authors.initials: D
authors.lastname: Crich
authors.affiliation: Institut de Chimie des Substances Naturelles, CNRS-ICSN UPR2301, Université Paris-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France. Electronic address: luis.bohe@cnrs.fr.
authors.forename: Luis
authors.initials: L
authors.lastname: Bohé
mesh_terms: D000080:Acetals / Q000138:chemical synthesis* / Q000737:chemistry; D002236:Carbohydrate Conformation; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D003500:Cyclization; D006031:Glycosylation; D008958:Models, Molecular; D013454:Sulfoxides / Q000737:chemistry*
chemical_list: D000080:Acetals; D002412:Cations; D013454:Sulfoxides
keywords: Cation clock; Glycosylation; Sulfenyl transfer; Sulfoxide donor; Tricyclic acetal