Iodine-Promoted Oxidative Annulation of Indoles with Trifluoromethyl <i>N</i>-Tosylhydrazone: Access to Trifluoromethylated Pyridazino[3,4-<i>b</i>]indoles

An efficient metal-free methodology for the construction of rarely reported trifluoromethylated pyridazino[3,4-<i>b</i>]indole scaffolds has been developed. The protocol was conducted with an operationally safe and bench-stable trifluoromethyl <i>N</i>-tosylhydrazone reagent in the iodine-promoted oxidative annulation of indoles in only one step, providing rapid access to a variety of trifluoromethylated pyridazino[3,4-<i>b</i>]indoles in good yields with good functional group compatibility. The findings could be used as a synthetic toolbox for the preparation of polycyclic indole-pyridazine fused <i>N</i>-heteroarenes for practical applications.