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

The halogen-bonding interaction between I and -iodosuccinimide (NIS) stabilized by a Lewis base (LB) has been explored. H NMR, nuclear Overhauser effect (NOE), and diffusion-ordered NMR spectroscopy (DOSY) suggest the generation of a 1:1:1 assembly, LB-I-NIS. In contrast, when -iodotrifluoromethanesulfonimide (INTf) is used instead of NIS, LB-I-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 I-NIS and the subsequent generation of an active iodinating species LB-I.