Isatin acylhydrazones with sterically hindered phenolic fragments: synthesis and structures

Isatin acylhydrazones with sterically hindered phenolic fragments were obtained. Their structures were determined using 1D and 2D 1H and 13C NMR spectroscopy and X-ray diffraction. The products synthesized by condensation of isatin and 1-(3,5-di- tert-butyl-4-hydroxybenzyl)-l H-indole-2,3-dione with 3-(3,5-di- tert-butyl-4-hydroxyphenyl)propiono-hydrazide exist as E- and Z-isomers about the C=N bond. E— Z isomerization takes place in boiling ethanol. The E-isomer of the condensation product from isatin and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionohydrazide was structurally characterized using X-ray diffraction: this isomer is a cis-conformer about the amide group and has a E-configuration about the N—N bond. According to data on the concentration dependence of the signals for the NH protons in the 1H NMR spectra, the acylhydrazones obtained are stabilized in solution by intra-and intermolecular hydrogen bonding.