Borsche-Drechsel Cyclization

E. Drechsel, J. Prakt. Chem. 38(2), 69 (1858); W. Borsche, M. Feise, Ber. 20, 378 (1904).

Formation of carbazole by acid-catalyzed rearrangement of cyclohexanone phenylhydrazone to tetrahydrocarbazole followed by oxidation:

N. Campbell, B. M. Barclay, Chem. Rev. 40, 361 (1947); W. Freudenberg, Heterocyclic Compounds 3, 298 (1952); P. Bruck, J. Org. Chem. 35, 2222 (1970). Cf. Bucherer Carbazole Synthesis; Fischer Indole Synthesis; Piloty-Robinson Synthesis.