Atropisomeric 1,2-dibenzoazaborines: Synthesis and Dynamic Studies

In this thesis project we have studied new atropisomeric molecules that have a nitrogen-boron bond in an aromatic cyclic system, namely the 1,2-dibenzoazaborine structure. We have synthesized molecules that have a stereogenic boron-aryl axis with different steric hindrance in the ortho position of the aryl ring (compounds 5). The synthesis reaction was optimized for compound 5a and then we introduced a chirality probe to follow the dynamic process by NMR (e.g. an ethyl group in product 5b and an isopropyl group in the product 5c). We have analyzed the molecules with NMR spectroscopy at variable temperature (VT), dynamic HPLC and kinetics studies to determinate the racemization energy barrier. Where possible (compound 5d), we have assigned the absolute configuration of the atropisomers by ECD (Electronic Circular Dichroism) methods and by TD-DFT (Time Dependent – Density Functional Theory) calculation.