4,4-Dimethyl-1-methylamino-1-phenyl-2-(substituted phenyldiazenyl)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 tetrafluoroborates) react with another molecule of substituted benzenediazonium tetrafluoroborate (in dichloromethane in the presence of anhydrous sodium acetate) to form substituted 4,4-bis(substituted phenyldiazenyl) derivatives 8. The second azo coupling is reversible. Derivatives 8 undergo either reverse cleavage of a diazonium ion or [1,3] sigmatropic rearrangement forming substituted formazane 9. In the case of the sequential use of two different diazonium tetrafluoroborates, the less electrophilic group splits off more easily. The structures of the products 9 were studied by means of X-ray, 1H, 13C, 19F and 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 a...
Diazonium exchange and migration of pivaloyl group upon azo coupling of β-enaminones
BERTOLASI, Valerio;
2013
Abstract
4,4-Dimethyl-1-methylamino-1-phenyl-2-(substituted phenyldiazenyl)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 tetrafluoroborates) react with another molecule of substituted benzenediazonium tetrafluoroborate (in dichloromethane in the presence of anhydrous sodium acetate) to form substituted 4,4-bis(substituted phenyldiazenyl) derivatives 8. The second azo coupling is reversible. Derivatives 8 undergo either reverse cleavage of a diazonium ion or [1,3] sigmatropic rearrangement forming substituted formazane 9. In the case of the sequential use of two different diazonium tetrafluoroborates, the less electrophilic group splits off more easily. The structures of the products 9 were studied by means of X-ray, 1H, 13C, 19F and 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 a...I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
