Influence of the Position of an Annular Nitrogen Atom on the Magnitude of the Rotational Barriers in Atropisomers of 1,8-Dihetarylnaphthalenes

Abstract

Five new atropisomerically chiral 1,8-dihetarylnaphthalenes were prepared by Pd(0)-catalyzed coupling reactions. Variable-temperature proton NMR spectra show those compounds with a 2'-pyridyl or 2'-pyrazinyl ring have a much lower energy barrier for rotation to interconvert conformational isomers than those with a 3'-pyridyl ring. Coalescence temperatures may differ by as much as 100 degrees C. The results of AM1 and PM3 computations indicate the preferred transition state for sigma-bond rotation places the annular nitrogen atom in the 2' or ortho position toward the face of the second hetaryl ring and not toward the naphthalene ring.

Recent trends in conformational analysis

“…The calculated PESs suggested that the preferred rotational mechanism was a delayed ring‐flip mechanism (Figure 9). Both AM1 and PM3 hamiltonians were used for the conformational analysis of some 1,8‐dihetarylnaphtalenes,83 and also in this case the calculations correctly simulated the trend of the activation energies derived from DNMR spectra.…”

Molecular balances for quantifying non-covalent interactions

“…15a-c). [49][50][51][52][53][54] The syn conformation was dominant for all of the compounds depicted in Figure 15a. The large upfield shielding of the 1 H-NMR methyl signals and the preference for the syn conformation can be attributed to the existence of favourable cation•••arene and CH•••areneinteractions between the positively polarised methyl substituents of one ring and electron-rich naphthalene face of the other.…”

Bis[oxo/thioxothiazolinyl] Aromatic Compounds - Synthesis and Conformational Assignment

“…The bis(oxo/thioxothiazolinyl) aromatic compounds are stereochemically interesting. While a large amount of information is available for nonheterocyclic, [3][4][5][6][7][8][9][10][11][12][13] and even for heterocyclic [14][15][16][17] atropisomers with two or more stereogenic C-C axes there are not many examples of atropisomers with two C(aryl)-N(heterocycle) stereogenic axes. Atropisomerically chiral systems with two chiral axes containing both aryls and heterocycles, namely 1,8 di-hetaryl-posite sides (antiparallel conformation) of the central aromatic ring.…”

“…Conformational assignment for the bis-thione atropisomers 1a,b-4a,b and bisone atropisomers 9a,b-12a,b was based on polarimetric re- [a] 'sults in analytical chiral chromatography on microcrystalline cellulose triacetate. The relationship conformation-1 H NMR chemical shifts, found for the bis-thiones and bis-ones was successfully applied for the conformational assignment of thione-one atropisomers not assigned by chiral liquid chromatography.naphthalenes [16,17] were recently investigated as model compounds for understanding the nature of electrostatic interactions involved during molecular recognition in systems such as proteins, nucleic acids, and host-guest pairs.…”

“…naphthalenes [16,17] were recently investigated as model compounds for understanding the nature of electrostatic interactions involved during molecular recognition in systems such as proteins, nucleic acids, and host-guest pairs.…”