O-Attack versus N-Attack: Electrophilic Halocyclization of Unsaturated Amides with Vinylic Halogen Substitution

Electrophilic iodocyclization of unsaturated amides with an internal vinylic halogen (Cl, Br, or I) substitution afforded exclusively the corresponding cyclic iminoketones via iodolactamization. On the other hand, amides having a terminal vinylic halogen substituent underwent iodolactonization only. Theoretical calculations revealed that the iodocyclization proceeds via the intramolecular iodonium ion transfer from the amide nitrogen to the C=C double bond.