Gunārs Duburs

Unusual cyclization of 1-thianaphthenone-3-dioxide-1,1 to a 1,5-diazabicyclo[3.3.1]nonane—a heterocyclic analogue of a Tröger's base

Abstract The synthesis of a novel heterocyclic system, bisbenzthieno[2,3- c :2′,3′- g ]-1,5-diazabicyclo[3.3.1]nonane-5,12-dioxide, is described. The structure of the product was confirmed by high resolution NMR techniques.

SPECTRAL AND QUANTUM-CHEMICAL STUDY OF NONEQUIVALENCE OF METHYLENE PROTONS IN 1,4-DIHYDROPYRIDINE DERIVATIVES*

Structural characteristics of 1,4-dihydropyridines influencing the nonequivalence of the diastereotopic methylene protons in substituents at positions 2 and 6 were studied. The combined effect of magnetically anisotropic groups and intramolecular hydrogen bonds leads to a considerable difference in the chemical shifts of the methylene protons of the AB system. The unusual reversible temperature evolution of these proton signals in monocyclic 1,4-dihydropyridines is associated with two simultaneous conformational processes. It was estimated that the energetically most favorable conformations are stabilized by an intramolecular СН⋯О hydrogen bond.

Electrochemical oxidation of hydrogenated indolizines and their precursors in chemical synthesis—quaternized pyridyldihydropyridines

The course of electrochemical and chemical oxidation of quaternized pyridyl dihydropyridines has been compared. The splitting off of the carboxylato group from the betaine structure as the substituent in position 4 of 1,4-dihydropyridine ring seems to be the decisive factor in the intramolecular cycloaddition forming indolizines during oxidation. The mechanisms of the electrochemical oxidation in acetonitrile of both tetrahydro- and dihydroindolizines have been studied using rrde voltammetry.

Correction to ‘Intramolecular hydrogen bonds in 1,4-dihydropyridine derivatives’

[This corrects the article DOI: 10.1098/rsos.180088.].

Intramolecular hydrogen bonds in 1,4-dihydropyridine derivatives

1,4-Dihydropyridine (1,4-DHP) derivatives have been synthesized and characterized by 1H, 13C, 15N nuclear magnetic resonance (NMR) spectroscopy, secondary proton/deuterium 13C isotope shifts, variable temperature 1H NMR experiments and quantum-chemical calculation. The intramolecular hydrogen bonds NH⋯O=C and CH⋯O=C in these compounds were established by NMR and quantum-chemical studies The downfield shift of the NH proton, accompanied by the upfield shift of the 15N nuclear magnetic resonance signals, the shift to the higher wavenumbers of the NH stretching vibration in the infrared spectra and the increase of the 1J(15N,1H) values may indicate the shortening of the N–H bond length upon intramolecular NH⋯O=C hydrogen bond formation.