TfOH-Catalyzed One-Pot Domino Reaction for Diastereoselective Synthesis of Polysubstituted Tetrahydrospiro[carbazole-1,3′-indoline]s

TfOH-catalyzed one-pot sequential reaction of indoles, acetophenones (cyclic ketones), and various 3-methyleneoxindolines in toluene afforded polysubstituted tetrahydrospiro­[carbazole-1,3′-indoline]­s in satisfactory yields. 1H NMR spectra and single-crystal structures indicated that the obtained tetrahydrospiro­[carbazole-1,3′-indoline]­s existing in an unusual trans-configuration. The reaction mechanism was believed to proceed with domino acid-catalyzed 3-alkenylation of indoles with acetophenones, Diels–Alder reaction of 3-alkyenylindoles with 3-methyleneoxindolines, and an acid-catalyzed diastereoisomerization process.