A Mild and Effective Method to Synthesize Carbazolones by CuI/l-Proline-Catalyzed Intramolecular Arylation

Abstract

Substituted carbazol-4-ones and 3,4-dihydrocyclo-pental indole-1-ones could be prepared in good yields via the intra­molecular coupling reaction of N-2-iodoaryl enaminones in the presence of CuI/l-proline under mild reaction conditions.

Key words

intramolecular cross-coupling - catalysis - 2-iodoaryl enaminone - l-proline

References and Notes

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12

Typical Experimental Procedure for the Synthesis of N -2-Iodoaryl Enaminone 4 A mixture of 2-iodobenzenamine (2.18 g, 10 mmol), 1,3-cyclohexanedione (1.12 g, 10 mmol), and TsOH·H₂O (190 mg, 1 mmol) in 30 mL of toluene was refluxed for 6 h. The cooled mixture was washed with H₂O and brine and was dried over Na₂SO₄. After removal of the solvent in vacuum, the residue was chromatographed on silica gel using PE-EtOAc (1:1) as the eluent to afford 3-(2′-iodophenyl-amino)cyclohex-2-enone (4a, 2.63 g, 84%)
Synthesis of Carbazol-4-one 3 A mixture of 3-(2′-iodophenylamino)cyclohex-2-enone (4a, 313 mg, 1 mmol), CuI (19 mg, 0.1 mmol), l-proline (23 mg, 0.2 mmol), and KOH (224 mg, 4 mmol) in 4 mL of DMSO was heated at 90 °C under nitrogen atmosphere for 24 h. The cooled solution was poured into H₂O and extracted with EtOAc. The combined organic layers were washed with brine and dried over Na₂SO₄. After removal of the solvent in vacuum, the residue was chromatographed on silica gel using PE-EtOAc (1:1) as the eluent to afford tetrahydro-carbazol-4-one (3a, 170 mg, 92%).