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
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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·H2 O (190 mg, 1 mmol) in 30 mL of toluene was refluxed for 6 h. The cooled mixture was washed with H2 O and brine and was dried over Na2 SO4 . 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 H2 O and extracted with EtOAc. The combined organic layers were washed with brine and dried over Na2 SO4 . 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%).