N-15, C-13 and H-1 NMR study of azo coupling products from diazonium saltsand 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-methylami no)pent-3-en-2-one gives a mixture of two isomers approaching the tautomeri c form of 4-amino-3phenylazopent-3-en-2-ones. The tautomeric form of the in dividual coupling products was determined by means of C-13 and N-15 NMR che mical shifts and J(N-15,II) coupling constants. With the help of TPPI-NOESY spectra it was possible to follow the rate of mutual exchange of four prot ons of NH groups in both isomers of 4-amino-3-(4-methylphenylazo)pent-3-en- 2-one. Copyright (C) 2000 John Wiley & Sons, Ltd.