Update on novel synthetic approaches towards the construction of carbazole nuclei: a review

Abstract

The carbazole scaffold is a significant entity in organic compounds due to its variety of biological and synthetic applications. Traditionally, carbazole skeletons have been synthesized either via the Grabe-Ullman method, Clemo-Perkin method or Tauber method. With the passage of time, these methods have been modified and explored to accomplish the synthesis of target compounds. These methods include hydroarylations, C-H activations, annulations and cyclization reactions mediated by a variety of catalysts to construct carbazole-based compounds. This brief review article intends to provide recent updates on important methodological developments reported for the synthesis of carbazole nuclei covering 2019-2023.

Fig. 1. N-Heterocyclic drugs and their structures.

Fig. 2. The structure of [9H-carbazole].

Fig. 3. Structures of carbazole containing natural compounds.

Scheme 1. Pd-catalyzed hydroarylation for synthesis of 2-iodo-1-aryl-9H-carbazoles.

Scheme 2. Mechanistic details for the synthesis of iodocarbazoles 16, 19 and 22.

Scheme 3. One-pot hydroarylation for carbazole synthesis.

Scheme 4. [4 + 2] Annulation for the synthesis of carbazole.

Scheme 5. One-pot cascade annulation reaction for synthesis of carbazole nucleus.

Scheme 6. Mechanistic details for the synthesis of functionalized carbazole 35.

Scheme 7. Synthesis of 4-hydroxy carbazole 38 and substituted carbazoles 40.

Scheme 8. Mechanistic details for the synthesis of carbazole derivative 38.

Scheme 9. Mechanistic details for the synthesis of carbazole derivative 40.

Fig. 4. Structure of carbazole derivative 41 and natural products (calothrixin B 41a, staurosporine 41b and carbazomycin A 41c) obtained by it.

Scheme 10. Rhodium catalyzed intramolecular benzannulation for synthesis of carbazole.

Scheme 11. Mechanistic details for the synthesis of carbazole derivative 43.

Scheme 12. Gold-catalyzed double benzannulation for synthesis of carbazole 45.

Scheme 13. AlCl₃-mediated annulation for the synthesis of carbazoles 49 and its derivatives.

Scheme 14. Pd-catalyzed and microwave-assisted synthesis of carbazole via C–H activation.

Scheme 15. Mechanistic details for the synthesis of carbazoles 55a and 55b.

Scheme 16. Pd-catalyzed C–H amidation for synthesis of 1-hydroxy carbazoles.

Scheme 17. Synthesis of carbazole via Au- and Mo-catalysis.

Scheme 18. Rh-catalyzed synthesis of carbazoles.

Scheme 19. Mechanistic details for the synthesis of carbazoles 64.

Scheme 20. Ni-catalyzed carboamination for the synthesis of carbazoles derivatives.

Scheme 21. Sunlight-mediated [3 + 2] cycloaddition for carbazole synthesis.

Scheme 22. Mechanistic details for the synthesis of carbazoles 71.