15N,13C and1H NMR study of azo coupling products from diazonium salts and enaminones

Reactions of diazonium salts with 4-substituted phenylaminopent-3-en-2-ones produce the corresponding 4-phenylimino-3-phenylhydrazonopentan-2-ones. On the other hand, the reaction of diazonium salt with 4-amino(or 4-methylamino)pent-3-en-2-one gives a mixture of two isomers approaching the tautomeric form of 4-amino-3-phenylazopent-3-en-2-ones. The tautomeric form of the individual coupling products was determined by means of 13C and 15N NMR chemical shifts and J(15N,H) coupling constants. With the help of TPPI-NOESY spectra it was possible to follow the rate of mutual exchange of four protons of NH groups in both isomers of 4-amino-3-(4-methylphenylazo)pent-3-en-2-one.