Novel aromatization reaction of enamines employing Pd (II) complex

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Enamines prepared from cyclohexanones, cyclohexane-1, 3-diones or tetralones led to aryl amines in one pot when treated with stoichiometric amount of palladium salts [PdCl_2 (MeCN)_2] in acetonitrile in the presence of triethylamine at rt or at elevated temperature in some cases for 5 min-2 h. Initial electrophilic attack of palladium chloride on the β-carbon of the enamines led to a σ-palladium species which triggered a series of reactions destined for aromatization to give aryl amines in good yields. The intervention of such a σ-palladium species has been attested by a trapping experiment. On the basis of this reaction mechanism, we have developed another new process capable of transforming acyclic compounds having 6-en-2-one frameworks to aryl amines when their enamines were treated under the similar conditions as above, featuring again the formation of σ-palladium species as the initial key intermediate.