title: Ring cleavage reactions of methyl α-D-allopyranoside derivatives with phenylboron dichloride and triethylsilane.
abstract: In the course of our studies on the regioselective carbon-oxygen bond cleavage of the benzylidene acetal group of hexopyranosides with a reducing agent, we found that a combination of a Lewis acid and a reducing agent triggered a ring-opening reaction of the pyranose ring of methyl α-D-allopyranosides. The formation of an acyclic boronate ester by the attachment of a hydride ion at C-1 indicated that the unexpected endocyclic cleavage of the bond between the anomeric carbon atom and the pyranose ring oxygen atom proceeded via an oxacarbenium ion intermediate produced by the chelation between O5/O6 of the pyranoside and the Lewis acid, followed by nucleophile substitution with a hydride ion at C1.
authors.affiliation: Niigata University of Pharmacy and Applied Life Sciences, 265-1 Higashijima, Akiha-ku, Niigata 956-8603, Japan. masaru@nupals.ac.jp
authors.forename: Masaru
authors.initials: M
authors.lastname: Kojima
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Yuusuke
authors.initials: Y
authors.lastname: Ito
authors.forename: Seiji
authors.initials: S
authors.lastname: Takeuchi
mesh_terms: D001896:Boron Compounds / Q000737:chemistry*; D006027:Glycosides / Q000138:chemical synthesis* / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*
chemical_list: D001896:Boron Compounds; D006027:Glycosides; D012821:Silanes; C512918:triethylsilane