Atropisomerism, Biphenyls, and Fluorine: A Comparison of Rotational Barriers and Twist Angles

Doing the twist: Atropisomerism of axially chiral biaryls is of increasing importance because the biaryl unit can be found in numerous biologically active natural products. Furthermore, biaryls are the most efficient reagents and ligands in asymmetric synthesis and the biphenyl unit belongs to the six or seven “privileged structures” in pharmaceutical research. Attention has to be paid to the factors which influence the electronic and geometric properties of the biaryl unit. Fluorine seems to be the ideal molecular tool for fine-tuning these properties.