Regiochemistry of radical cyclisations (6-exo/7-endo and 7-exo/8-endo) of N-(o-alkenylphenyl)-2,2-dichloroacetamides

Abstract

N-[o-(Alk-1-enyl)phenyl]-2,2-dichloroacetamides, when treated with 2.2 mol equiv. of Bu₃SnH in the presence of a catalytic amount of azoisobutyronitrile, gave quinolin-2(1H)-one (6-exo closure) and/or 2H-1-benzazepin-2-one (7-endo closure) systems. In general, the 6-exo cyclisation is favoured over the 7-endo closure, unless a large group such as phenyl is present at the 1-position of the alkene. N-[o-(1-Methylethenyl)phenyl]acetamide congeners underwent a 6-exo closure followed by rearrangement to give 1,5-dihydro-4-methyl-2H-1-benzazepin-2-ones. A similar treatment of N-[o-(prop-2-enyl)phenyl] acetamide derivatives gave 2H-1-benzazepin-2-ones (7-exo) and/or 1-benzazocin-2(1H)-ones (8-endo).