The acid-catalyzed condensation of 1-benzylindole with acetone in the presence of N-phenylmaleimide gave a tetrahydrocarbazole, (4,5,10,10b-tetrahydro-5-methyl-2-phenyl-10-(phenylmethyl)pyrrolo[3,4-a]carbazol e-1,3[2H, 3aH]-dione (1), as the major product and a novel spiro compound, 1′,3,4,4′-tetrahydro-1′,1′,3,3-tetramethyl-4,4′-bi s(phenylmethyl)-1,3′(2H, 2′H)-spiro[cyclopent[b]indole] (2), as the minor product. The structure of the spiro compound was determined by an X-ray crystallographic determination. The acid-catalyzed condensation of 1-benzylindole with acetone in the absence of N-phenylmaleimide gave a bisindole, (1,1′-bis(phenylmethyl)-3,3′-(1-methylethylidene)diindole (3), as the major product and the spiro-compound as the minor product.
Bibliographical noteFunding Information:
We are indebted to the duPont Company for a 1988 summer research fellowship to MJK, to the Wayland E. Noland Research Fellowship Fund for financial support to MJK and SV, and to the Lando-SOHIO program of the chemistry department for a 1988 summer research fellowship to SJF.