C-3 arylation protocols of quinoxalin-2(1H)-ones with arylhydrazines and aryl boronic acids under metal-, photocatalyst- and light-free conditions using non-toxic K2S2O8.
We report an efficient and atom-economic method of C-3 functionalization reaction of quinoxalin-2(1H)-ones with 4-hydroxycoumarins, 4-hydroxy-6-methyl-2-pyrone, and 2-hydroxy-1,4-naphthoquinone via free radical cross-coupling pathway under metal-free conditions. tert-Butylhydropreoxide (TBHP) smoothly promotes...
Scheme 1. Direct trifluoromethylation of quinoxalin-2(1H)-ones with CF 3 SO 2 Na under metal-free conditions. Scheme 2. Plausible mechanism for trifluoromethylation of quinoxalin-2(1H)ones with CF 3 SO 2 Na/PhI(OTFA) 2 . *À furnishes the desired product.Scheme 7. Trifluoromethylation of quinoxalin-2(1H)-ones under under photocatalyst-free conditions. Scheme 8. Electrochemical trifluoromethylation of quinoxalin-2(1H)-ones. Scheme 9. Plausible mechanism for electrochemical trifluoromethylation of quinoxalin-2(1H)-ones with Zn(CF 3 SO 2 ) 2 . Scheme 10. Trifluoromethylation of quinoxalin-2(1H)-ones using (NH 4 ) 2 S 2 O 8 . Scheme 11. Plausible mechanism for trifluoromethylation of quinoxalin-2(1H)-ones with CF 3 SO 2 Na/(NH 4 ) 2 S 2 O 8 . Scheme 12. Trifluoromethylation of imidazo[1,2-a]pyridines with CF 3 SO 2 Na. Scheme 13. Plausible mechanism for AgNO 3 catalyzed trifluoromethylation of imidazo[1,2-a]pyridines with CF 3 SO 2 Na/ TBHP. Scheme 14. Trifluoromethylation of imidazoheterocycles with CF 3 SO 2 Na. Scheme 15. Plausible mechanism for Cu(OAc) 2 catalyzed trifluoromethylation of imidazo[1,2-a]pyridines with CF 3 SO 2 Na/ TBHP. Scheme 16. Trifluoromethylation of imidazoheterocycles with photocatalyst.
We report an efficient protocol for the synthesis of 3‐trifluoromethylquinoxalin‐2(1H)‐ones, 3‐trifluoromethylimidazo[1,2‐a]pyridines and 3‐(trifluoromethyl)‐2H‐indazoles under metal‐, photocatalyst‐, light‐ and electrochemical‐free conditions. The combination of Langlois’ reagent (sodium triflinate) with the oxidant (NH4)2S2O8 in DMSO: H2O (10 : 1) works as an efficient reagent system to promote this free radical trifluoromethylation reaction. The trifluoromethyl radical generated by the oxidation of sodium triflinate with (NH4)2S2O8 attacks on to the C‐3 position of quinoxalin‐2(1H)‐ones, imidazo[1,2‐a]pyridines and 2H‐indazoles; and the excess SO4•− completes the reaction furnishing their respective 3‐trifluoromethyl derivatives in very good to excellent yields. Radical scavenging experiments with (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO), butylated hydroxy toluene (BHT), and 1,1‐diphenylethylene also prove the participation of radical.
A new solvent cum reagent system comprising of water extract of banana ash and dimethylsulfoxide (WEB‐DMSO) has been engaged for the first time to promote the aldol type condensation reaction of aldehydes with ethyl diazoacetate. The condensation reaction has smoothly undergone producing a range of α‐diazo‐β‐hydroxy esters in good to excellent yields. The solvent system has been reused up to five times without loss of its catalytic activity. Further, two one‐pot sequential reactions have been developed in the same reaction medium. First, the methodology has been extended to synthesize β‐keto esters through Pd catalyzed 1,2‐hydrogen migration. Secondly, β‐keto esters have been converted to imidazo[1,2‐a]pyridine‐3‐carboxylates by using N‐bromosuccinimide and 2‐aminopyridines in a one‐pot fashion.
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