Atropisomerism and Axial Chirality in Heteroaromatic Compounds

The chapter “Atropisomerism and axial chirality in heteroaromatic compounds” provides a summary of the present knowledge of this important topic. The structure of the chapter is: first a detailed description of the methods used to study atropisomerism, from X-ray diffraction to theoretical calculations (14 items), then the application to different compounds according to the nature of the central bond. Rotation about a C–C bond (5–5, 5–6 and 6–6 rings), rotation about a C–N bond (azoles, oxo- and thioxo-five-membered rings, azines), rotation about an N–N bond (5–5, 5–6 and 6–6 rings), rotation about ortho-ortho’-linked compounds, rotation about N-metal bonds, multiple rotations, to end with axial chiral synthesis. In conclusion, a phenomenon that was discovered in 1922 for diphenic acids and that was extended to heterocycles in 1931 by Adams shows eighty years later to be very active, being expected to grow in importance because it is related to asymmetric synthesis, to materials and to biological properties.