Gw. Gribble et al., Intramolecular Diels-Alder reactions of 4H-furo[3,4-b]indoles. New syntheses of benzo[a]carbazoles and benzo[c]carbazoles, SYN COMMUN, 29(4), 1999, pp. 729-747
Furoindoles 7 and 16 undergo smooth intramolecular Diels-Alder reactions to
afford, after dehydration, hydrolysis, and oxidation, benzocarbazoles 11 a
nd 21, respectively.