Perfluoroalkylation of Aryl-N,N-dimethyl Hydrazones Using Hypervalent Iodine(III) Reagents or Perfluoroalkyl Iodides

Abstract

Radical trifluoromethylation of aryl N,N-dimethyl hydrazones using TBAI as an initiator and Togni’s reagent as a trifluoromethyl radical source is described. Cascades proceed via electron-catalysis; this approach is generally more applicable to hydrazone perfluoroalkylation using perfluoroalkyl iodides as the radical precursors in combination with a base under visible-light initiation.

α‐Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1‐(Dialkylamino)‐1,2,3‐triazoles

“…Alternatively, deprotonation of Int-II may occur first leading to the corresponding radical anion, which would undergo oxidation to 5'. [23] A light on/off experiment confirmed the necessity of continuous irradiation for the reaction to proceed; moreover, measurement of the quantum yield of the reaction to form 5 c (F = 0.18) suggests that a radical chain process cannot be a predominant path. [24] Finally, the plausible utility of the triazole products obtained as precursors for mesoionic 1-(dialkylamino)-1,2,3triazol-4-ylidene ligands was evaluated.…”

“…Deprotonation would re‐establish the C‐N double bond of the hydrazone moiety leading to 5′ , which ultimately cyclizes to the observed 1,2,3‐triazole 5 . Alternatively, deprotonation of Int‐II may occur first leading to the corresponding radical anion, which would undergo oxidation to 5′ [23] . A light on/off experiment confirmed the necessity of continuous irradiation for the reaction to proceed; moreover, measurement of the quantum yield of the reaction to form 5 c ( Φ =0.18) suggests that a radical chain process cannot be a predominant path [24]…”

Radical‐Mediated Formal C(sp2)–H Functionalization of Aldehyde‐Derived N,N‐Dialkylhydrazones

“…Recently, Studer and co‐workers have proposed an alternative, metal‐free method for the trifluoromethylation of aromatic‐aldehyde‐derived N , N ‐dimethylhydrazones with use of the Togni reagent ( 3 ) and tetrabutylammonium iodide (TBAI) as an initiator (Scheme ). These reactions require higher temperatures (boiling point of ethyl acetate) than the previous Cu‐catalyzed process.…”

“…Among possible reaction pathways, it is suggested that the reaction may proceed through photochemical activation (UVA light) of a donor–acceptor (EDA) complex of the reacting partners (the electron‐rich hydrazone and the electron‐deficient perfluoroalkyl iodide) . Another photochemical protocol for the perfluoroalkylation of N , N ‐dimethylhydrazones, suggested to proceed through a radical chain mechanism, has also been proposed by Studer (Scheme ).…”

Organocatalytic Group Transfer Reactions with Hypervalent Iodine­ Reagents

“…Scheme 23 TBAI-promoted trifluoromethylation/cyclization of α,β-unsaturated amides with Togni reagent II A very similar discrepancy in the mechanistic interpretation occurs for the TBAI-promoted C-H azidation of aldehydes with 1-azido-1,2-benziodoxol-3(1H)-one (18), described by Saito and co-workers in 2015 (Scheme 24), 46 and a highly similar C-H trifluoromethylation of benzaldehyde N,N-dimethylhydrazones with 10, developed by Studer and co-workers in 2017 (Scheme 25). 47 Saito and co-workers are inclined toward the generation of IN 3 , which would then effect the azidation, whereas Studer and co-workers postulate a radical chain pathway through a free CF 3…”