title: 5-Exo versus 6-endo cyclization of nucleoside 2-sila-5-hexenyl radicals: reaction of 6-(bromomethyl)dimethylsilyl 1',2'-unsaturated uridines.
abstract: The mode of cyclization of 2-sila-5-hexen-1-yl radicals generated from 6-(bromomethyl)dimethylsilyl-1',2'-unsaturated uridines was investigated. In contrast to the case of the 2'-unsubstituted 6-silicon-tethered substrate (4), which undergoes exclusive 6-endo-cyclization, reactions of the 2'-substituted (Me, CO2Me, OBz, and Cl) derivatives (14, 20, 22, and 24) uniformly proceeded in preferential or exclusive 5-exo-mode. The Tamao oxidation of the resulting cyclized products was also carried out to synthesize the corresponding 1'-C-hydroxymethyl derivatives.
authors.affiliation: School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Ogamino
authors.forename: Hideaki
authors.initials: H
authors.lastname: Mizunuma
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kumamoto
authors.forename: Shingo
authors.initials: S
authors.lastname: Takeda
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Haraguchi
authors.forename: Kazuo T
authors.initials: KT
authors.lastname: Nakamura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sugiyama
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Tanaka
mesh_terms: D003500:Cyclization; D005609:Free Radicals / Q000737:chemistry; D008968:Molecular Conformation; D009705:Nucleosides / Q000138:chemical synthesis / Q000737:chemistry*; D017646:Organosilicon Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D014529:Uridine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D009705:Nucleosides; D017646:Organosilicon Compounds; D014529:Uridine