Electrochemical synthesis of 5-trifluoroethyl dihydrobenzimidazo[2,1-a] isoquinolines from pendent unactivated alkenes via radical relay

Visible Light-Induced Radical Cascade Difluoromethylation/Cyclization of Unactivated Alkenes: Access to CF2H-Substituted Polycyclic Imidazoles

“…Colorless oil (43 mg, 76% yield); purified by silica gel column chromatography (hexanes/ethyl acetate mixtures 5:1–1:1 (v/v)); 1 H NMR (400 MHz, CDCl 3 ) δ 8.35–8.32 (m, 1H), 7.87–7.82 (m, 1H), 7.50–7.42 (m, 2H), 7.40–7.28 (m, 4H), 5.78 (tdd, J = 56.2, 3.5, 3.1 Hz, 1H), 4.46 (dd, J = 12.8, 2.2 Hz, 1H), 4.32–4.27 (m, 1H), 3.60–3.55 (m, 1H), 2.22–1.96 (m, 2H); 13 C NMR (101 MHz, CDCl 3 ) δ 148.4, 144.1, 136.6, 134.9, 130.6, 128.6, 127.9, 126.3, 126.0, 123.1, 122.8, 119.9, 115.9 (t, J = 239.7 Hz), 109.1, 44.8, 37.9 (t, J = 21.2 Hz), 33.2 (dd, J = 6.5, 3.5 Hz); 19 F NMR (376 MHz, CDCl 3 ) δ −(115.22–116.20) (m, 1F), −(117.13–118.15) (m, 1F); HRMS (ESI, m / z ) [M + H + ] calcd for C 17 H 15 F 2 N 2 : 285.1198, found 285.1199. The spectral data were in accordance with the literature …”

“…In 2021, Guo and co-workers disclosed the synthesis of CF 2 H-substituted polycyclic benzimidazoles via photocatalytic radical difluoromethylation/cyclization of N -alkenoxyl 2-aryl benzimidazoles in continuous flow. 25 In 2023, the synthesis of 5-(2,2-difluoroethyl)-5,6-dihydrobenzo[4,5]imidazo[2,1- a ]isoquinoline from N -alkenyl 2-aryl benzimidazole through the electrochemical radical process was reported by Li’s group 26 ( Scheme 1 a). Notably, a variety of protocols for the cyclization of benzimidazoles with olefins at the C-2 position have been continuously developed.…”

Electrochemical trifluoroalkylation/annulation for the synthesis of CF3-functionalized tetrahydroquinolines and dihydroquinolinones

“…11 Compared to the classic Umemoto's reagent, Togni's reagent, Ruppert's reagent and Baran's reagent, Langlois’ reagent (NaSO 2 CF 3 ) is a cheaper and easily handled trifluoromethylating reagent. 9 c ,12,13…”

Metal-free polychloromethylation/cyclization of unactivated alkenes towards ring-fused tricyclic indolones and benzoimidazoles

“…1) 15 and such structures can also be constructed by bifunctionalization of alkenes. 16 After the successful construction of polychloromethylated ring-fused indolones, we set our goal to synthesize polychloromethylated polycyclic benzoimidazoles. As shown in Table 3, the trichloromethylative cyclization of substituted 1-(pent-4-enyl)-1 H -benzo[ d ]imidazoles gave the corresponding trichloromethylated tricyclic benzo[ d ]pyrido[1,2- a ]imidazoles in 53–77% yields ( 5a–5e ).…”