Synthesis of dihydrocarbazoles via (4+2) annulation of donor-acceptor cyclopropanes to indoles was written by Liu, Changhui;Zhou, Li;Huang, Wenbo;Wang, Man;Gu, Yanlong. And the article was included in Tetrahedron in 2016.Reference of 4769-96-4 This article mentions the following:
Dihydrocarbazoles were synthesized through a novel [4+2] annulation of donor-acceptor cyclopropanes (DACs) to indoles. This reaction was performed in ethanol by using para-toluenesulfonic acid as catalyst. Mechanism of this reaction might involve the following three steps: (i) an electrophilic ring-opening reaction of the DACs with indoles, in which C3 position of indole acts as a nucleophilic site, (ii) an intramol. dehydration induced ring-closing reaction occurs that offers a spiro intermediate, and (iii) a following 1,2-migration which leading to a dihydrocarbazole scaffold. Otherwise, dihydroisoindole can also be constructed by replacing the indole component with pyrrole as nucleophile. In the experiment, the researchers used many compounds, for example, 6-Nitro-1H-indole (cas: 4769-96-4Reference of 4769-96-4).
6-Nitro-1H-indole (cas: 4769-96-4) belongs to indole derivatives. In addition to tryptophan, indigo, and indoleacetic acid, numerous compounds obtainable from plant or animal sources contain the indole molecular structure. More than 200 indole derivatives have already been marketed as drugs or are under advanced stages of clinical trials.Reference of 4769-96-4
Referemce:
Indole alkaloid derivatives as building blocks of natural products from Bacillus thuringiensis and Bacillus velezensis and their antibacterial and antifungal activity study,
Preparation of Indole Containing Building Blocks for the Regiospecific Construction of Indole Appended Pyrazoles and Pyrroles