NMR STUDY OF ATROPISOMERIC 1-ARYL-2- IMINOAZACYCLOALKANES AND 1-ARYL-2-OXOAZACYCLOALKANES

JIMENA E. DÍAZ; LILIANA R. ORELLI

Aveiro

Congreso; IV Iberoamerican NMR Meeting; 2012

Sociedad Química de Portugal

NMR STUDY OF ATROPISOMERIC 1-ARYL-2- IMINOAZACYCLOALKANES AND 1-ARYL-2-OXOAZACYCLOALKANESJimena E. Díaza, Liliana R. Orelliaa Departamento de Química Orgánica. Facultad de Farmacia y Bioquímica. Universidad de Buenos Aires.CONICET. Junín 956. (1113) Buenos Aires, Argentina.jediaz@ffyb.uba.arAtropisomerism 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.1 Our group has discovered and investigated some new families of atropisomeric heterocycles.21-Aryl-2-iminoazacycloalkanes 1 are cyclic amidines where the sp2 nitrogen is exocyclic. Spontaneous hydrolysis of 1 yields 1-aryl-2-oxoazacycloalkanes 2. When the aryl moiety is 2-substitued (Ar*), the heterocycles adopt a non-coplanar, thus chiral conformation, allowing for the existence of atropoisomers.Complete assignment of the 1H and 13C NMR resonances of compounds 1,2 was achieved based on 2D spectral correlations. We also discuss the features of the 1H NMR spectra which show diastereotopic geminal hydrogens, therefore giving indirect evidence of molecular asymmetry.The ground state geometry of compounds 1,2 was optimized with DFT/B3LYP 6-311++dp calculations, confirming the non-coplanar conformation which entails the existence of atropoisomers. Direct evidence of their existence was provided by the 1H NMR spectra recorded in the presence of an enantiopure chiral solvating agent. We also present some preliminary dynamic NMR experiments (variable temperature NMR) aimed at determining the enantiomerization barriers of compounds 1. 1.Among others: (a) A.C. Spivey, D.P. Leese, F. Zhu, S.G. Davey, R.L. Jarvest, Tetrahedron, 2004, 60 4513-4525 and references therein.2. (a) M.B. García, S. Grilli, L. Lunazzi, A. Mazzanti, L.R. Orelli, J. Org. Chem. 2001, 66, 6679-6684 (b) M.B. García, S. Grilli, L. Lunazzi, A. Mazzanti, L.R. Orelli, Eur. J. Org. Chem. 2002, 23, 4018-4023 (c) M.L. Magri, N. Vanthuyne, C. Roussel, M.B. García, L.R. Orelli, J. Chromatogr. A 2005, 1069, 203-208 (d) J.E. Díaz, M.B. García, L.R. Orelli, J.Mol.Struct. 2010 982, 50-56.