Synthesis by a Pschorr reaction from diazotized α-(2-naphthyl)-2-aminocinnamic acid: Cook, J. Chem. Soc. 1931, 2524. From diphenylmethylsuccinic anhydride: Hewett, J. Chem. Soc. 1936, 599. By double ring closure of β-benzohydrylglutaric acid: Newman, Joshel, J. Am. Chem. Soc. 60, 487 (1938). From 4-keto-1,2,3,4-tetrahydrophenanthrene: Bachmann, Edgerton, ibid. 62, 2970 (1940).