4,4-Dimethyl-1-methylamino-1-phenyl-2-(substituted phen-
yldiazenyl)pent-1-en-3-ones (prepared upon azo coupling of
4,4-dimethyl-1-methylamino-1-phenylpent-1-en-3-one 6a
with the corresponding benzenediazonium tetrafluorobor-
ates) react with another molecule of substituted benzenedi-
azonium tetrafluoroborate (in dichloromethane in the pres-
ence of anhydrous sodium acetate) to form substituted 4,4-
bis(substituted phenyldiazenyl) derivatives 8. The second
azo coupling is reversible. Derivatives 8 undergo either re-
verse cleavage of a diazonium ion or [1,3] sigmatropic re-
arrangement forming substituted formazane 9. In the case of
the sequential use of two different diazonium tetrafluoro-
borates, the less electrophilic group splits off more easily. The
structures of the products 9 were studied by means of X-ray,
1H,
13C,
19Fand 15N NMR and MALDI HRMS analyses. The
formazans 9 exhibit a reduced mobility of the phenyl group
adjacent to the pivaloyl group, giving rise to anisochronism
of proton and carbon atoms, to eventually form conformers.
The reduced mobility was observed by means of NMR spec-
troscopy. A temperature dependence of the spectral behav-
iour was also studied