Photoredox‐Catalzyed Halo‐trifluoromethylation of 1,7‐Enynes for Synthesis of 3,4‐Dihydroquinolin‐2(1H)‐ones

Abstract

An efficient photoredox‐catalyzed halo‐trifluoromethylation reaction of 1,7‐enynes has been developed under mild conditions. This photocatalytic protocol provides an efficient and functional strategy leading to CF3− and halogen‐containing 3,4‐dihydroquinolin‐2(1H)‐ones from a wide range of 1,7‐enynes through two different radical pathways. The reaction mechanism was proposed based on the control experiments.magnified image

New Visible‐Light‐Triggered Photocatalytic Trifluoromethylation Reactions of Carbon–Carbon Multiple Bonds and (Hetero)Aromatic Compounds

“…Methodology 2, only useful for the synthesis of Clcontaining (E)-3,4-dihydroquinolin-2(1 H)ones, employs trifluoromethanesulfonyl chloride (CF 3 SO 2 Cl), as both CCF 3 radicala nd Cl atom sources, fac-Ir(ppy) 3 as photocatalyst and acetonitrile as solvent under blue LEDs irradiation;t his methodology also exhibitedawides ubstrate scope (Scheme42). The authors [87] accomplished severalc ontrol experiments and suggest the radicalm echanism depicted in Scheme 43. Initially, blue light excites the Mes-Acr + photocatalyst affording Mes-Acr + *w hich oxidizesC F 3 SO 2 Na yielding CCF 3 radicals, SO 2 and acridine radical.…”

“…1,7-Enynes have been used as substrates fort he simultaneous photocatalyzed incorporationo fh alogena nd CF 3 groups by Yuan, Li, and Guo. [87] This photocatalytic protocol provides a strategyl eading to CF 3 -a nd halogen-containing 3,4-dihydroquinolin-2(1H)-ones from aw ide range of 1,7-enynes through two different radical pathways. One pathway involves the use of Langlois reagent CF 3 SO 2 Na as as ource of CF 3 radicals and mesityl acridinium as photocatalyst, and another the employment of fac-Ir(ppy) 3 as photocatalyst and triflyl chloride CF 3 SO 2 Cl as source of CF 3 radicals.…”

“…In 2018 Bu, Cai, and co-workers [87,88] have accomplishedt he photocatalyzed trifluoromethylation of alkynesw ith subsequent cyclization of the aryl alkynoates towards the synthesis of coumarins with trifluoromethyl groups. The photocatalyst employed was Ir(ppy) 3 ,C F 3 SO 2 Cl as source of CF 3 radicals, in MeCN as solvent, with K 2 CO 3 as base, irradiating with blue LEDs.…”

“…Guo and co-workers [87] developed two methodologiesf or the photoredox-catalyzed halo-trifluoromethylation of 1,7enynes towards the synthesiso f3 ,4-dihydroquinolin-2(1 H)ones.M ethodology 1, useful for the synthesis of Cl or Brcontaining (E)-3,4-dihydroquinolin-2(1 H)ones, employs CF 3 SO 2 Na as the CCF 3 radical source, N-chlorophthalimide or Nbromophthalimide as the Cl or Br atom source, respectively, Nmethyl-9-mesityl acridinium perchlorate (Mes-Acr + )a sp hotocatalysti na cetonitrile as solventu nder blue LEDs irradiation; selected examples of the substrate scope are shown in Scheme 41. Methodology 2, only useful for the synthesis of Clcontaining (E)-3,4-dihydroquinolin-2(1 H)ones, employs trifluoromethanesulfonyl chloride (CF 3 SO 2 Cl), as both CCF 3 radicala nd Cl atom sources, fac-Ir(ppy) 3 as photocatalyst and acetonitrile as solvent under blue LEDs irradiation;t his methodology also exhibitedawides ubstrate scope (Scheme42).…”

“…Proposed mechanism for the photoredox-catalyzed chloro-trifluoromethylationo f1 ,7-enynes for the synthesis of (E)-3,4-dihydroquinolin-2(1 H)ones using methodologies1and 2. [87] imide affording the desired reactionp roduct. The mechanism proposed for method 2i sc omparable to method 1b ut involving an Ir III/ Ir IV photoredox cycle for generating CCF 3 radicals and Cl À .T he CCF 3 radical upon addition to the CÀCd ouble bond of the 1,7-enyne, finally forms the cyclized radical adduct A which can be oxidized by reactionw ith CF 3 SO 2 Cl or Ir IV ,g enerating carbocation B that is subsequently attacked by Cl À generating the reaction product.…”