Trifluoroethanol as a Unique Additive for the Chemoselective Electrooxidation of Enamines to Access Unsymmetrically Substituted NH‐Pyrroles

Abstract

An electrochemical method for the synthesis of unsymmetrically substituted NH-pyrroles is described. The synthetic strategy comprises ac hallenging heterocoupling between two structurally diverse enamines via sequential chemoselective oxidation, addition, and cyclization processes. As eries of aryl-and alkyl-substituted enamines were effectively cross-coupled from an equimolar mixture to synthesize various unsymmetrical pyrrole derivatives up to 84 %y ield. The desired cross-coupling was achieved by tuning the oxidation potential of the enamines by utilizing a" magic effect" of the additive trifluoroethanol (TFE). Additionally, extensive computational studies reveal the unique role of TFE in promoting the heterocoupling process by regulating the activation energies of the reaction steps through H-bonding and CÀH•••p interactions.I mportantly,t he developed electrochemical protocol was found to be equally efficient for the homocoupling of enamines to form symmetric pyrroles up to 92 %y ield.

Cu(I)‐Catalyzed Coupling Reactions of β‐Nitrostyrene, 1,3‐Dicarbonyl compound & Aryl amine: An Efficient Method For the Synthesis of Polysubstituted Pyrroles

“…Furthermore, a similar set of synthesis were obtained through ball milling in presence of silica gel [25] . An alternative method for pyrrole synthesis using electrochemical techniques has been reported [26] . Various catalysts, like nano‐NiFe 2 O 4 , [27] nano‐NiO, [28] tungsten complex, [29] amberlyst‐15, [30] nano CoFe 2 O 4 supported antimony (III)catalyst, [31] Heterogeneous Fe‐MIL‐101 catalysts, [32] nano CuO catalyst [33] and [NMPH]CH 3 SO 3 [34] have been utilized for the synthesis of substituted pyrroles.…”

“…[25] An alternative method for pyrrole synthesis using electrochemical techniques has been reported. [26] Various catalysts, like nano-NiFe 2 O 4 , [27] nano-NiO, [28] tungsten complex, [29] amberlyst-15, [30] nano CoFe 2 O 4 supported antimony (III)catalyst, [31] Heterogeneous Fe-MIL-101 catalysts, [32] nano CuO catalyst [33] and [NMPH]CH 3 SO 3 [34] have been utilized for the synthesis of substituted pyrroles. There are several synthetic procedures reported for the synthesis of polysubstituted pyrroles providing flexibility based on the starting ingredients and desired end products.…”