Mechanism of Hypervalent Iodine Promoted Fluorocyclization of Unsaturated Alcohols: Metathesis via Double Acids Activation.

Lewis/Bronsted acid activation plays a key role in hypervalent iodine reagent-mediated reactions. In addition to generally accepted cis-activation or trans-activation, this study reveals another important Lewis/Bronsted acid activation mode, the double-activation. Different from the generally proposed iodine(III)iranium SN2 mechanism, the hypervalent difluoro-iodoarene-promoted fluorocyclization of unsaturated alcohol prefers to undergo the metathesis mechanism via an iodine(III)-π intermediate.