Mechanisms of Formation and Rearrangement of Benziodoxole-Based CF and SCF Transfer Reagents.

Togni's benziodoxole-based reagents are widely used in trifluoromethylation reactions. It has been established that the kinetically stable hypervalent iodine form (I-CF) of the reagents is thermodynamically less stable than its acyclic ether isomer (O-CF). On the other hand, the trifluoromethylthio analogue exists in the thermodynamically stable thioperoxide form (O-SCF), and the hypervalent form (I-SCF) has been elusive. Despite the importance of these reagents, very little is known about the reaction mechanisms of their syntheses, which has hampered the development of new reagents of the same family. Herein, we use density functional theory calculations to understand the reasons for the divergent behaviors between the CF and SCF reagents. We demonstrate that they follow different mechanisms of formation and that the metals involved in the syntheses (potassium in the case of the trifluoromethyl reagent and silver in the trifluoromethylthio analogue) play key roles in the mechanisms and greatly influence the possibility of their rearrangements from the hypervalent (I-CF, I-SCF) to the corresponding ether-type form (O-CF, O-SCF).