Reactions of 1,2-Bis(1H-indol-2-yl)ethane: Formation of Indolo[2,3-c]carbazole and Cyclohept[1,2-b:5,4-b′]bisindole Derivatives

1,2-Bis(1H-indol-2-yl)ethane (9) has been prepared and converted into indolo[2,3-c]carbazole (8) using palladium acetate in refluxing acetic acid. Reaction of 9 with CoF3 in hot TFA led to isolation of cyclohept[1,2-b:5,4-b′]bisindole derivatives 11 and 12, which could be elaborated into further derivatives. Treatment of 9 with orthoesters, aldehydes and ketones under acidic conditions afforded additional bisindoles containing a seven-membered ring.