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

Ramandeep Kaur; Harcharan Singh; Srinivasarao Arulananda Babu

doi:10.1055/a-2056-2363

Synthesis, Inhaltsverzeichnis

Synthesis 2023; 55(21): 3535-3567
DOI: 10.1055/a-2056-2363

special topic

C–H Bond Functionalization of Heterocycles

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

Ramandeep Kaur

,

Harcharan Singh

,

Srinivasarao Arulananda Babu ∗

Abstract

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Abstract

We 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.

Key words

bidentate directing group - carbazoles - C–H activation - β-C(sp²)–H functionalization - nitrogen heterocycles - palladium catalysis

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Referenzen

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16 Wang and Wang reported^5s the CuI-catalyzed C–H alkoxylation of benzamides and proposed a mechanism for the C–H alkoxylation via the Cu(II) species. It is believed that DBU functions as an efficient organic base in promoting the Cu(II) species generation step with the removal of the NH proton from the amide moiety (and it also may have an additional role).
17 CCDC 2233500 (8b) and CCDC 2233501 (21a) contain the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures

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