Atropisomerism of aromatic carbamates

Abstract

ortho-Haloarylcarbamates like 1-4 show a high rotational barrier about the N-aryl bond of up to 91.6 kJmol-1 as found for 1, which was determined by 2D exchange NMR spectroscopy (EXSY). It was further demonstrated that the height of the barrier not only depends on the substituents at the axis of chirality, but is also influenced by electronic effects. In a tight spot: The depicted N-aryl-N-alkylcarbamate (Bn=benzyl) exists as four atropo-diastereomers at room temperature due to hindered rotation about the N-aryl and N-C(O) bonds. By using 2D exchange NMR spectroscopy (EXSY), the height of the rotational barriers could be determined and compared to those of three related compounds. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.