Halogen-Bonding Interaction between I2 and N-Iodosuccinimide in Lewis Base-Catalyzed Iodolactonization.

The halogen-bonding interaction between I2 and N-iodosuccinimide (NIS) stabilized by a Lewis base (LB) has been explored. 1H NMR, nuclear Overhauser effect (NOE), and diffusion-ordered NMR spectroscopy (DOSY) suggest the generation of a 1:1:1 assembly, LB-I2-NIS. In contrast, when N-iodotrifluoromethanesulfonimide (INTf2) is used instead of NIS, LB-I5+-LB is generated. On the basis of these results in combination with density functional theory (DFT) calculations, we propose a mechanism for the formation of I2-NIS and the subsequent generation of an active iodinating species LB-I+.