Isatin acylhydrazones with sterically hindered phenolic fragments: synthesis and structures

Abstract

Isatin acylhydrazones with sterically hindered phenolic fragments were obtained. Their structures were determined using 1D and 2D 1 H and 13 C NMR spectroscopy and X ray diffraction. The products synthesized by condensation of isatin and 1 (3,5 di tert butyl 4 hydroxybenzyl) 1H 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 1 H NMR spectra, the acylhydrazones obtained are stabilized in solution by intra and intermolecular hydrogen bonding.

A catalyst-free and easy nucleophilic addition of certain isatins to sterically hindered 2,6-di-tert-butyl-4-methylenecyclohexa-2,5-dienone

“…These conditions 25,26 allows in situ generation of the highly reactive p-quinone methide 4 which immediately undergoes addition of corresponding isatin 1a-d with formation of a carbonnitrogen bond (Scheme 2). It should be noted here that the reaction takes place despite the hindrance due to the methyl group at the 7 position of the isatin heterocycle.…”