Selective fluorination of alkyl C–H bonds via photocatalysis

Abstract

We report the generation of cationic N-radicals from Selectfluor® via energy transfer with anthraquinone as a photocatalyst for the fluorination of unactivated C-H bonds.

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp3)‐Substrates

“…The groups of Tan [92] and Chen [93] reported photocatalytic fluorination of unactivated C-H bonds by use of Selectfluor® as a fluorine source and anthraquinone (60) or acetophenone (61), respectively, as photocatalyst (Scheme 39). Despite their structural similarity, the ketone catalysts were suggested to perform different roles in the two studies.…”

Visible light-promoted metal-free sp3-C–H fluorination

“…The Inoue, 9 Tang, 10 and Hartwig 11 groups have also shown that N -oxyl radical and silver salts can catalyze or promote C–H fluorination. More recently, photolytic activation methods have also been reported by Britton, 12 Lectka, 8c and Tan 13 using decatungstate, 1,2,4,5-tetracyanobenzene (TCB), and anthraquinone (AQN) as the catalyst, respectively.…”

“…8c,13 To test this hypothesis and to further exclude the possibility that Selectfluor reacted with acetophenone to form a transient reactive species not detectable by UV, we examined if CFL-irradiation could also promote unimolecular C–H abstraction of monoarylketones. Indeed, CFL-irradiation induced the Norrish type II cleavage and Norrish–Yang cyclization of valerophenone ( 22 ) ( n →π* transition λ max ~325 nm) to give 23 – 26 (Fig.…”

“…21 The unimolecular photoreaction of 22 further suggest that acetophenone can function as a C–H abstraction catalyst instead of a photosensitizer in activating Selectfluor toward C–H abstraction. 8d,13 …”

Anthraquinones as Photoredox Catalysts for the Reductive Activation of Aryl Halides

“…[16,18] Not surprisingly, different quinone derivatives have been used for photo-oxidative transformations under visible light. [19][20][21][22] Fukuzumi reported the photoredox catalytic conversion of benzene to phenol with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) under visible-light irradiation. [23] Itoh and subsequently Yuan reported the trifluoromethylations of arenes and heteroarenes with anthraquinone-2-carboxylic acid [24] and abstraction or C-C bond-forming reactions.…”