Cyclization of α-haloamide with internal double bond by use of the low-valent metal complex
作者:Miwako Mori、Izumi Oda、Yoshio Ban
DOI:10.1016/s0040-4039(00)85827-x
日期:1982.1
Is an Iodine Atom Almighty as a Leaving Group for Bu<sub>3</sub>SnH-Mediated Radical Cyclization? The Effect of a Halogen Atom on the 5-Endo-trig Radical Cyclization of <i>N</i>-Vinyl-α-halo Amides
The effect of a halogen atom as a leaving group on Bu3SnH-mediated 5-endo-trig radical cyclization of N-(cyclohex-l-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 Bu3SnCl or Bu3SnF as an additive. The cyclization of an alpha-iodo amide in the presence of Bu3SnF could be applied to a short-step synthesis of lycoranes featuring sequential 5-endo-trig and 6-endo-trig radical cyclizations.