Pd(II)-Catalyzed Directing-Group-Aided C–H Arylation, Alkylation, Benzylation, and Methoxylation of Carbazole-3-carboxamides toward C2,C3,C4-Functionalized Carbazoles

Abstract

AbstractWe report the Pd(II)-catalyzed β-C–H arylation, alkylation, benzylation, and methoxylation of carbazole-3-carboxamide and carbazole-2-carboxamide substrates, assisted by the bidentate directing groups 8-aminoquinoline or 2-(methylthio)aniline, and construction of C2,C3,C4-functionalized carbazole motifs. The Pd(II)-catalyzed β-C–H arylation reaction was attempted using different directing groups such as 8-aminoquinoline, 2-(methylthio)aniline, 4-amino-2,1,3-benzothiadiazole, 4-methoxyquinolin-8-amine, and butan-1-amine. Through optimization of the reactions, 8-aminoquinoline and 2-(methylthio)aniline were found to be suitable directing groups and, especially, 2-(methylthio)aniline was found to be an efficient directing group in the Pd(II)-catalyzed β-C–H arylation, alkylation, and methoxylation of carbazole-3-carboxamide, carbazole-2-carboxamide substrates. An ample number of β-C–H arylated, alkylated, benzylated, and methoxylated carbazole-3-carboxamides were synthesized. The structures of representative β-C(2)–H arylated carbazole and β-C(2)–H methoxylated carbazole motifs were unequivocally confirmed by single-crystal X-ray structure analysis. Given the wide range of applications of carbazoles in chemistry, materials sciences, and medicinal chemistry and there have been constant efforts for developing new methods for synthesizing functionalized carbazoles. This work contributes to the expansion of the library of C2,C3,C4-functionalized carbazole motifs through a Pd(II)-catalyzed directing-group-aided site-selective β-C–H activation and functionalization of carbazole-3-carboxamides.