Heterocyclic analogs of pleiadiene 76. Synthesis and tautomeric conversions of mono- and disubstituted perimidines with electron-withdrawing substituents in the naphthalene fragment

Abstract

A series of new mono-and disubstituted perimidines with electron-withdrawing substituents in the naphthalene fragment has been synthesized. Their prototropic annular tautomerism has been investigated by 1 H NMR spectroscopy.We reported previously on the extremely slow annular prototropic tautomerism of derivatives of 2-trifluoromethylperimidine containing a formyl, acetyl, or p-toluenesulfonyl group in position 6(7) [2,3]. This phenomenon is expressed in the 1 H and 19 F NMR spectra of these compounds by the simultaneous observation of signals of both tautomers in low polarity solvents at room temperature and even on heating to 120-130 o C. It is assumed that the reason for this is the low basicity of these compounds in combination with spatial screening of both heteroatoms not only from the side of the 2-CF 3 substituent but also from the hydrogen atoms in positions 4 and 9.In the light of this it seemed of interest to investigate the prototropic tautomerism of 2-tertbutylperimidine (1) and also of the product of its 6(7)-acylation. It was expected that, not being an acceptor but being large, the tert-butyl group may hinder transfer of proton.We obtained compound 1 by the action of pivaloyl chloride on 1,8-naphthalenediamine. On acylation with acetic acid in PPA at 70-75 o C the isomeric 6(7)-and 4(9)-diacetyl derivatives of 2-tert-butylperimidine 2 and 3 were synthesized in 66 and 11% yield respectively.The 1 H NMR spectrum of 2-tert-butylperimidine (1) in CDCl 3 was unresolved. A strongly broadened peak of the ortho protons (H-4 and H-9) and a multiplet signal of the remaining aromatic protons indicated a somewhat slow prototropy. However, unlike other perimidines, the picture of the spectrum is practically