Recyclizations of 2‐aminobenzylimines and thioaroylhydrazones of N‐substituted N‐hydroxy‐3‐oxobutanamides

Abstract

A universal scheme is proposed for the molecular design of heterocyclic recyclizations by replacing the exocyclic hydroxyl groups in e x o -t r i g-ring-chain tautomeric molecules with substituted amines or hydrazines. The practical applicability of this approach is demonstrated by the condensations of 5-hydroxy-5-methyl-3-isoxazolidinones with thioaroyl-hydrazines and 2-aminomethylaniline. The condensation products were studied by modern 1 H, 1 3 C and 1 5 N NMR spectroscopic methods using three solvents: CDCl 3 , DMSO [D 6 ] and CD 3 CN. The solvent was found to have a strong effect to the relative amounts of the tautomers.

Recent Developments in the Ring‐Chain Tautomerism of 1,3‐Heterocycles

“…According to 1 H, 13 C and 15 N NMR measurements, the equilibria involved (Z) and (E) isomers of the enamine open forms (A) together with the benzylaminosubstituted isoxazolidine (D) and the tetrahydroquinazoline cyclic forms (C), the proportions of which varied, depending on the solvents [CDCl 3 , (CD 3 ) 2 SO and CD 3 CN]. [32] The (Z) and (E) isomers of the corresponding enamine open form were also detected in the ring-chain equilibrium of 2-methyl-2-(morpholinocarbonylmethyl)-1,2,3,4-tetrahydroquinazoline in (CD 3 ) 2 SO. [33] Scheme 23…”