Diazonium Exchange and Migration of Pivaloyl Group upon Azo Coupling of β‐Enaminones

Abstract

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

A simple, enaminone-based approach to some bicyclic pyridazinium tetrafluoroborates

“…The mechanism of the exchange is described in [32]. Its application to the reaction of 4g with 4-nitrobenzenediazonium ion (Scheme 6) can explain the formation of the mixture of pyridazinium salts 5k + 5m : 4g can react with another molecule of the diazonium salt either to give the bishydrazone intermediate Im and subsequently the pyridazinium salt 5n (in the sense of Scheme 5) or it can undergo an ipso attack to form the intermediate Ip , consisting of 4-methoxy and 4-nitrophenyldiazenyl groups.…”

pH-Induced Linkage Isomerism of Pd(II) Complexes: A Pathway to Air- and Water-Stable Suzuki–Miyaura-Reaction Catalysts

“…THF was dried by distillation from benzophenone/sodium prior to use. The synthesis of 4,4-dimethyl-1-pyridin-4-yl-pentane-1,3-dione (ligand L1 ) and 4,4-dimethyl-1-pyridin-3-yl-pentane-1,3-dione (ligand L2 ) follow previously described procedures. ,, …”

“…The synthesis of 4,4-dimethyl-1-pyridin-4-yl-pentane-1,3-dione (ligand L1) and 4,4-dimethyl-1-pyridin-3-yl-pentane-1,3-dione (ligand L2) follow previously described procedures. 39,45,46 The 1 H NMR and 13 C NMR spectra were acquired on a Bruker Fourier 300 spectrometer equipped with a 1 H/ 13 C 5 mm probe and referenced to the solvent residual-1 H peaks. All spectra were acquired at 298 K. The NMR solvents were purchased from Euriso-Top or Deutero GmbH and used as received.…”