Copper nanoparticle-catalyzed synthesis of N-arylated indoles, carbazoles, and N-alkylated indoles

Abstract

This article describes the synthesis of amide-based mono-phosphines: [o-Ph₂P(C₆H₄)C(O)N(H)C₆H₄(o-OR)] (R = CH₃ (Me), C₂H₅ (Et), or CH(CH₃)₂ (ⁱPr)), which further react with CuX salts to afford dimeric copper complexes having the general formula [Cu₂(μ²-X)₂{o-Ph₂P(C₆H₄)C(O)N(H)C₆H₄(o-OR)}-κ²-P,O}₂] (1, X = Cl, R = Me; 2, X = Br, R = Me; 3, X = I, R = Me; 4, X = Cl, R = Et; 5, X = Br, R = Et; 6, X = I, R = Et; 7, X = Cl, R = ⁱPr; 8, X = Br, R = ⁱPr; and 9, X = I, R = ⁱPr). Complex 6 efficiently catalyzed the N-arylation and N-alkylation of indoles with aryl and alkyl halides, affording a series of N-substituted indole derivatives. This outstanding performance can be attributed to the high catalytic activity of in situ generated Cu nanoparticles (Cu@6) from the reaction of complex 6 with a KOH base. Moreover, the catalytic process involved sequential steps of oxidative addition, transmetallation, and reductive elimination, ultimately yielding indole products.