A rotationally hindered and thus stereogenic biaryl axis is the structurally and stereochemically decisive element of a steadily growing number of natural products, chiral auxiliaries, and catalysts. Thus, it is not surprising that significant advances have been made in the asymmetric synthesis of axially chiral biaryl compounds over the past decade. In addition to the classic approach (direct stereoselective aryl-aryl coupling), innovative concepts have been developed in which the asymmetric information is introduced into a preformed, but achiral-that is, symmetric or configurationally labile-biaryl compound, or in which an aryl--C single bond is stereoselectively transformed into an axis. This Review classifies these strategies according to their underlying concepts and critically evaluates their scope and limitations with reference to selected model reactions and applications. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed.

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

1,1‘-Binaphthyl Dimers, Oligomers, and Polymers: Molecular Recognition, Asymmetric Catalysis, and New Materials†

Chromium− and Manganese−salen Promoted Epoxidation of Alkenes

London dispersion, which constitutes the attractive part of the famous van der Waals potential, has long been underappreciated in molecular chemistry as an important element of structural stability, and thus affects chemical reactivity and catalysis. This negligence is due to the common notion that dispersion is weak, which is only true for one pair of interacting atoms. For increasingly larger structures, the overall dispersion contribution grows rapidly and can amount to tens of kcal mol(-1) . This Review collects and emphasizes the importance of inter- and intramolecular dispersion for molecules consisting mostly of first row atoms. The synergy of experiment and theory has now reached a stage where dispersion effects can be examined in fine detail. This forces us to reconsider our perception of steric hindrance and stereoelectronic effects. The quantitation of dispersion energy donors will improve our ability to design sophisticated molecular structures and much better catalysts.

London Dispersion in Molecular Chemistry—Reconsidering Steric Effects

Although chiral phosphines have enjoyed a longtime
popularity in the design of enantioselective
catalytic systems, there has been a recent renaissance
in the use of nitrogen ligands for this same
purpose.1 This renaissance partly arises from several
distinct advantages presented by nitrogen-containing
ligands. First, they can often be employed in catalytic
processes where the use of phosphines may be
incompatible with the reaction conditions. Second,
many nitrogen ligands are now available in enantiomerically
pure form. Third, ligands that bind through
nitrogen are known to coordinate with a wide variety
of metal ions, and considerable progress has been
made in understanding the role which these ligands
play in affecting catalytic processes.

Kenji Suzuki

Papers

Rational design of Mn-salen catalyst (2): Highly enantioselective epoxidation of conjugated cis olefins

Titanium–Salan‐Catalyzed Asymmetric Epoxidation with Aqueous Hydrogen Peroxide as the Oxidant

Titanium—Salan-Catalyzed Asymmetric Epoxidation with Aqueous Hydrogen Peroxide as the Oxidant.