Premium
Diazonium Exchange and Migration of Pivaloyl Group upon Azo Coupling of β‐Enaminones
Author(s) -
Šimůnek Petr,
Bertolasi Valerio,
Macháček Vladimír
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201300534
Subject(s) - chemistry , electrophile , azo coupling , smiles rearrangement , dichloromethane , conformational isomerism , diazonium compounds , medicinal chemistry , molecule , nuclear magnetic resonance spectroscopy , anhydrous , polymer chemistry , stereochemistry , organic chemistry , catalysis , solvent
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, 1 H, 13 C, 19 F and 15 N 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 spectroscopy. A temperature dependence of the spectral behaviour was also studied.