Pushing radical cyclization from regioselective to regiospecific: cyclization of amidyl radicals controlled by vinylic halogen substitution.
Efficient and regiospecific 6-exo, 7-endo, 7-exo, and even 8-endo amidyl radical cyclizations can be accomplished by the direct reactions of unsaturated N-H amides if they bear a vinylic halogen (Cl, Br, I) substituent. This remarkable halogen-substitution effect could be rationalized in terms of lone pair-lone pair electron repulsion between the N radical and the vinylic halogen atom, in addition to the well-known steric and radical-stabilizing effect. [reaction: see text]
Hu
Tianshun
T
Shanghai Istitute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. China.
Shen
Meihua
M
Chen
Qian
Q
Li
Chaozhong
C