Polycarbonyl heterocycles. VI. A ¹³C‐N.M.R. study on the structure of H‐bonded ion pair: 3‐Benzoyl‐pyrrolidine Derivatives/Piperidine

Abstract

Comparison of spectral data obtained from 13C n.m.r. analyses for compound 1–6 implies the structure of H‐bonded ion pairs 2, 4, 6. In the formation of ion pair 2 the exo‐enol tautomeric form “b” is involved, on the other hand, the endoenolic form “c” is a main tautomer producing the H‐bonded ion pair 4. A stereospecific transformation of compound 5 leads to formation of complex 6 with aliphatic amine.

Pyrrolidinetrione Derivatives: Synthesis And Applications in Heterocyclic Chemistry

“…29 13 C NMR spectroscopy was a valuable technique for studying the behavior of carbon atoms involved in intramolecular interactions. 48 Comparison of spectral data obtained from 13 C NMR analysis revealed, that the exo-enol form a was involved in the formation of ion pairs of 1-phenyl-4-(phenylhydroxymethylene)-pyrrolidine-2,3,5-trione with piperidine (44), but the endoenol form b was the main tautomer during the ion pair formation between 1-phenyl-3-(phenyl-hydroxymethylene)pyrrolidine-2-thioxo-4,5-dione with piperidine (45) ( Figure 9). Additional proof of the above conclusion was provided from the IR spectra.…”

“…Pyrrolo[3,4-c]pyrazole, Pyrrolo[3,4-c]-1,4-diazepine and Pyrrolo[3,4-f]-1,5-diazocine A general route to pyrrolo[3,4-c]pyrazoles 49 and 50, 51,52 pyrrolo[3,4-e]-1,4-diazepines 51 and 52,[53][54][55] as well as pyrrolo[3,4-f]-1,5-diazocines 53 and 54 56 is based on regioselective attack of binucleophiles at positions C-6 and C-3 under conditions excluding competitive formation of the appropriate salts 48. The pyrrolo[3,4-c]pyrazole derivatives 49 and 50 were obtained by cyclocondensation of the appropriate pyrrolidinetrione with phenyl hydrazine in boiling ethanol.51,52 Pyrrolo[3,4-f]-1,4-diazepines 51 and 52 were prepared in a similar way by reaction of 22 or 33 with ethylene diamine, but at room temperature in ethanol.…”

Study on the Reactions of 3‐Benzoyl‐2,4,5‐pyrrolidinetrione with aliphatic diamines, phenylhydrazine, semicarbazide and guanidine derivatives

“…The reactions were carried out in ethanolic solution adjusted to pH 7 by addition of acetic acid to prevent the clevage of pyrroloring in alkaline medium. It was proved that 1 has exo-enol [9] structure which determines its strong acidic (pK, 2.63 [lo]) properties and modifies the reaction pathway by revealing three following steps: i) formation of salt, ii) splitting of the salt by the excess of amine and formation on the benzoyl carbonyl group the enamine with exocyclic double bond stabilized by intramolecular hydrogen bond with carbonyl oxygen at position 4' or 2' (two possible structure) or imine with endocyclic double bond, iii) cyclocondensation on the nonamide carbonyl group. The progress of the reaction depends on the basicity of diamino reagents.…”