作者:L. Yu. Ukhin、L. V. Belousova、Zh. I. Orlova、S. V. Shishkina、O. V. Shishkin
DOI:10.1023/a:1020956614588
日期:——
The reactions of aminals, the Mannich bases, and azomethines derived from substituted salicylaldehydes were studied. Derivatives of tetrahydrocyclopenta[b]- and hexahydro-cyclohepta[b]chromenes and substituted 2,2'-spirobichromenes were prepared from aminals, and substituted hexahydroxanthenes were synthesized from the Mannich bases. Azomethine derivatives of 5-nitrosalicylaldehyde and aliphatic amines react with cyclohexanone to form 4a-amino-7-nitro-2,3,4,4a-tetrahydro-1H-xanthenes. 4a-Morpholino-7-nitro-9-phenylethynyl-1,2,3,4,9,9a-hexahydroxanthene was studied by X-ray diffraction analysis.
The structures of the main tautomers of the Schiff base of salicylaldehyde with ethylamine and its protonated species have been studied by ESI MS, FT-IR as well as H-1, C-13 and N-15 NMR methods. The spectroscopic methods have provided clear evidence that the Schiff base exists in acetonitrile solution in a low barrier O center dot center dot center dot H center dot center dot center dot N imine-oxo tautomeric form. This form is also energetically favourable as indicated by PM5 calculations. This untypical Schiff base form is stabilized by a resonance effect with the nitro group and the interaction of the intramolecular hydrogen-bonded proton with acetonitrile via a intermolecular hydrogen bond. The protonated Schiff base exists in solution as imine-hydroxy form stabilized by intermolecular hydrogen bonds with nitro groups and solvent molecules. (C) 2010 Elsevier B.V. All rights reserved.