Simple Photo-Induced Trifluoromethylation of Aromatic Rings

Abstract

The trifluoromethylation of various aromatic compounds with Umemoto reagent II (2,8-difluoro-5-(trifluoromethyl)-5H-dibenzo[b,d]thiophen-5-ium triflate) proceeded in moderate to good yields under simple photo-irradiation conditions without any catalyst, additive, or activator. UV-Vis and NMR spectral analyses indicated that pre-formation of an electron donor-acceptor complex between the trifluoromethylating reagent and the substrate, as proposed in previous studies, is not essential for generation of the trifluoromethyl radical. Instead, the radical appears to be formed by simple photo-activation of the Umemoto reagent.

Recent Advances in Direct C−H Trifluoromethylation of N‐Heterocycles

“…In the same year, Egami, Hamashima, and their group [87] described the CÀ H trifluoromethylation of aromatic rings under photo-irradiation conditions in the absence of any catalyst or additive with Umemoto reagent (2,8-difluoro-5-(trifluoromethyl)-5H-dibenzo[b,d]thiophen-5-ium triflate) as a CF 3 radical source (Scheme 87). Pyridines, as well as pyrroles, were compatible under the reaction conditions.…”

Site‐Selective Trifluoromethylation Reactions of Oligopeptides

“…In 2010 Sodeoka and co‐workers disclosed an efficient Cu‐catalyzed electrophilic trifluoromethylation featuring Togni reagent II as the CF 3 source for the modification of a vast array of indoles, including the Trp derivative Ac‐Trp‐OMe . More recently, the radical trifluoromethylation of Ac‐Trp‐OMe has been achieved by using Ummemoto reagents as practical sources for the production of the corresponding radical trifluoromethyl species by reaction with the electron‐donor N ‐methylmorpholine (NMM) or under photo‐irradiation conditions . Likewise, the organic semiconductor mesoporous graphitic carbon nitride (mpg‐CN) has proven a sustainable, yet highly efficient photocatalyst for the C2‐trifluoromethylation of Boc‐Trp‐OEt with both Langlois reagent and CF 3 SO 2 Cl .…”

“…Driven by their experience in photoredox catalysis, Lei and co‐workers have recently reported a visible‐light induced Ir‐catalyzed radical C2‐trifluoromethylation of a variety of Trp‐containing short peptides with Langlois reagent . Unlike previous examples, the method was found applicable for the selective modification of a number of di‐, tri‐ and tetrapeptides bearing amino acids with unprotected alcohols such as Tyr, Thr and Ser, or the carboxyl group such as Asp, among others (Scheme ). The robustness of the protocol was illustrated by the gram‐scale trifluoromethylation of Ac‐Trp‐OMe and, importantly, an aqueous solvent system could be utilized, albeit higher yields were obtained in neat acetonitrile.…”

Recent Advances in Rapid Synthesis of Non-proteinogenic Amino Acids from Proteinogenic Amino Acids Derivatives via Direct Photo-Mediated C–H Functionalization

“…Trifluoromethylation of tryptophans from plentiful trifluoromethyl synthons in photochemistry has been widely investigated (Scheme 27). Trifluoromethanesulfonyl chloride, 2-(trifluoromethylsulfonyl)ethanone, and Umemoto reagent II have been used in the trifluoromethylation reactions independently by Blechert's group [60], Li's group [61], Hamashima and Egami's group [62], since 2015. NaSO 2 CF 3 as a stable, inexpensive, and easy-handling trifluoromethyl synthon has been applied in the trifluoromethylation of tryptophans catalyzed by the mesoporous graphitic carbon nitride (mpg-CN) [63] and iridium complex [64], respectively.…”