Michael-Type Addition Reactions of Some Enamines to Arylidenepyrazolones

The reaction of the arylidenepyrazolones (1_b-d) with l-morpholinocyclohexene (E₂) in refluxing acetonitrile leads to the less substituted alkylated enamines 3_b-d. On the other hand, the more substituted alkylated enamines 2_a-d are formed when 1_a-d react under the same conditions with l-piperidinocyclohexene (E₁). The nature of the enamine is crucial. Nucleophilic attack of the enamine on the α, β-unsaturated carbonyl system of 1 gives rise to a zwitterionic intermediate which through α -proton loss leads to different Michael-type adducts depending on the enamine.