Studies of Enamines. II. The Reaction of 4-(1-Piperidyl)- and 4-(1-Pyrrolidinyl)-3-penten-2-ones with Aryl Isocyanates

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Abstract
The reaction of aryl isocyanates with enamino ketones, derived from acetylacetone and secondary amines such as piperidine and pyrrolidine, has been investigated. At room temperature, enamino ketones react with phenyl, p-chlorophenyl and p-tolyl isocyanate to give 1:2 adducts, 3,5-diarylcarbamoyl derivative. In solution, these adducts exist in general as a mixture of two tautomers, 3-penten-2-one and 4-penten-2-one, the ratio depending on the solvent. Under reflux in benzene, the reaction of enamino ketones with phenyl isocyanate gives 4-amino-6-methyl-1-phenyl-5-phenylcarbamoylpyrid-2-one and its 3-phenylcarbamoyl derivative; the former is also obtained by heating the 1:2 adduct. On the other hand, 4-(1-pyrrolidinyl)-3-penten-2-one reacts with 1-naphthyl isocyanate to afford the 1:1 adduct, 5-(1-naphthylcarbamoyl)-4-penten-2-one.