DNMR STUDY OF ATROPISOMERIC 1-ARYLPIPERIDIN-2-IMINES

JIMENA E. DÍAZ; ANDREA MAZZANTI; MICHELE MANCINELLI; LILIANA R. ORELLI

Carlos Paz

Conferencia; 13th Latin American Conference on Physical Organic Chemistry; 2015

Universidad Nacional de Córdoba

Atropisomerism is a property of some molecules that exist as enantiomeric forms due to restricted rotation around certain single bonds, which behave as chiral axes. In the last years, there is a growing interest for the development of stable non-biaryl atropisomers, due to their potential employment in stereoselective synthesis. Our group has discovered and investigated some new families of atropisomeric heterocycles.1,2. 1-Arylpiperidin-2-imines 1 are cyclic amidines where the sp2 nitrogen is exocyclic. When the aryl moiety is 2-substitued (Ar*), the two rings adopt a non-coplanar conformation, allowing for the existence of an atropisomeric pair. In this work we present the determination of the enantiomerization barriers of compounds 1 by means of variable temperature NMR and lineshape analysis (DNMR). We discuss the influence of the stereoelectronic nature of the substituents on the magnitude of the enantiomerization barriers. We compare these results with those of 1-arylpirrolydin-2-imines 2, lower homologs of compounds 1, to analyze the effect of the ring size. We additionally report the enantiomerization barrier of compound 3, in which the NH moiety is substituted by oxygen, in order to address the influence of the exocyclic heteroatom. The conformational ground states and the structures of the transition states were calculated using DFT methods. The calculated barriers are compared with the experimental values. 1 Díaz, J. E.; Gruber, N.; Lunazzi, L.; Mazzanti, A.; Orelli, L. R. Tetrahedron 67, 9129 (2011) 2 Díaz, J. E.; Vanthuyne, N.; Rispaud, H.; Roussel, C.; Vega, D.; Orelli, L. R. J. Org. Chem. 80, 1689 (2015)