Protocols for the Syntheses of 2,2′-Bis(indolyl)arylmethanes, 2‑Benzylated Indoles, and 5,7-Dihydroindolo[2,3‑b]carbazoles

The electrophilic substitution reaction of 4,7-dihydroindole with aryl-aldehydes as an electrophilic partner followed by an oxidation step to deliver 2,2′-bis­(indolyl)­arylmethanes was studied for the first time. The reaction afforded regioselectivity at the 2,2′-positions of indole in an operationally simple and inexpensive procedure with a variety of substrates. To the best of our knowledge, this is the first set of examples of 2,2′-bis­(indolyl)­arylmethanes obtained in a substituent-free manner. A facile method from dipyrromethanes to the corresponding 2-benzylindoles was also reported. In addition, 2,2′-bis­(indolyl)­arylmethanes were converted to 5,7-dihydroindolo­[2,3-b]­carbazoles.