Theoretical study of the iodine-catalyzed nucleophilic addition by halogen bond

The iodine-catalyzed nucleophilic addition of pyrrole to acetone has been studied by density functional theory at the level of Lan12DZ*. It has been shown that the first iodine molecule appears to have a remarkable catalytic effect on this reaction by halogen bond between carbonyl oxygen and iodine molecule, but the second one does not improve the reaction largely. In general, the nucleophilic addition at the C(2) site of pyrrole is more favorable than that at the C(3) site; however, this trend is not prominent or even changed in acetronitrile solvent for the indole system, which is consistent with the experimental result by Bandgar.