title: Is an iodine atom almighty as a leaving group for Bu(3)SnH-mediated radical cyclization? The effect of a halogen atom on the 5-endo-trig radical cyclization of N-vinyl-alpha-halo amides.
abstract: The effect of a halogen atom as a leaving group on Bu(3)SnH-mediated 5-endo-trig radical cyclization of N-(cyclohex-1-enyl) alpha-halo amides was examined. The cyclization of alpha-chloro amides occurred with a high degree of efficiency, whereas the corresponding alpha-iodo congeners gave only limited quantities of cyclization products. A detailed study revealed that these phenomena could be attributed to the initial conformations of alpha-halo amides. The cyclizing ability of alpha-iodo amides can be restored with Bu(3)SnCl or Bu(3)SnF as an additive. The cyclization of an alpha-iodo amide in the presence of Bu(3)SnF could be applied to a short-step synthesis of lycoranes featuring sequential 5-endo-trig and 6-endo-trig radical cyclizations.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kanazawa University, Takara-machi, Kanazawa 920-0934, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Tamura
authors.forename: Hana
authors.initials: H
authors.lastname: Matsukida
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyao
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Takeda
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ishibashi