Propiolamidines I. Syntheses of N,N′-Disubstituted Phenylpropiolamidines and New Routes to 5-N-Substituted Amino-3-phenylisoxazoles and 5-N-Substituted Amino-1,3-diphenylpyrazoles

Abstract N,N′-Disubstituted phenylpropiolamidines were synthesized from phenylacetylene and carbodiimides. They were inert toward nucleophiles in a neutral or basic medium, but reactive in an acidic one. They reacted in the presence of hydrogen chloride with hydroxylamine, hydrazine, and arylhydrazines to give 5-N-substituted amino-3-phenylisoxazoles, 5-N-substituted amino-3-phenylpyrazole and 5-N-substituted amino-1-aryl-3-phenylpyrazoles, respectively, by nucleophilic addition followed by cyclization. The reaction mechanism is discussed on the basis of the structures of these heterocyclic compounds.