Domino Reaction for Synthesis of Spiro[pyrazole‐4,5′‐pyrrolo[3,4‐c]carbazoles] and Spiro[pyrrolo[3,4‐c]carbazole‐5,5′‐thiazoles].

The concentrated hydrochloride catalyzed reaction of 3‐(indol‐3‐yl)maleimides with (E)‐4‐arylidene‐5‐methyl‐2‐phenylpyrazol‐3‐ones in acetonitrile at room temperature afforded unexpected Michael addition product in high yields, which could be easily converted to the cis/trans‐diastereoisomers of spiro[pyrazole‐4,5′‐pyrrolo[3,4‐c]carbazoles] with the nearly 2 : 1 ratios by further oxidation with DDQ. On the other hand, the similar one‐pot two‐step reaction of 3‐(indol‐3‐yl)maleimides with (E)‐5‐arylidene‐2‐phenylthiazol‐4‐one predominately gave cis‐diastereoisomers of spiro[pyrrolo[3,4‐c]carbazole‐5,5′‐thiazoles] in satisfactory yields. The reaction mechanism included domino acid catalyzed Michael addition and DDQ oxidative coupling process [ABSTRACT FROM AUTHOR]