121056-58-4Relevant articles and documents
Synthesis and Reactions of Oligomethylene-Clamped 1H-Azepines and Benzene Imines. Their Valence Tautomeric Equilibrium and Nitrogen Stereochemistry
Lange, Walter,Tueckmantel, Werner
, p. 1765 - 1776 (2007/10/02)
Syntheses of the clamped 1H-azepines and benzene imines, 6a, 5b/6b, and 5c, and of some of their N-derivatives are described, and the positions of their valence tautomeric equilibria are examined.The N-methyl and N-chloro substituents favour the closed valence tautomer whereas the N-methoxycarbonyl group shifts the equilibrium towards the open isomer.The N-trimethylsilyl group also exerts a slight effect in the latter sense.Low temperature 1H and 13C NMR examination of 5b/6b demonstrates that the free activation enthalpy of the valence tautomerization must be below 5 kcal/mol (21 kJ/mol), but that the nitrogen inversion can be frozen, with the syn isomer (i.e., H on N syn relative to the C=C double bonds) predominating. 1H NMR shifts of the N-substituents and, for 14a, preliminary X-ray data indicate that the N-substituents of the above benzene imines prefer syn orientation. 6a rearranges on silica gel to give 33 which is silylated to yield 34.Action of sodium methoxide on 14a leads to 37 which is again chlorinated at nitrogen and treated with sodium methoxide to produce 40 and 41.Plausible mechanisms for these transformations are proposed. - Key Words: 1H-Azepines/ Arene imines/ Valence tautomerism/ Nitrogen inversion/ N-Chloroamines
