The chirality of atropisomers is originating from restricted rotations along chemical single bonds. Atropisomers are rotamers in which the barrier to rotation about a single σ bond is so high, that the separate rotamers (stereoisomers) can be isolated. The use of atropisomers is not limited to ligands and catalysts. In particular atropisomers have nowadays been synthesized for API application. Due to their stability, which is, in most cases, the result of large steric hindrance around the axis of chirality and energy barriers with values > 40 kcal/mol Health Authorities have approved such drugs. In order to synthesize atropisomers often a Cinchona alkaloid scaffold is used.

These chiral Cinchona alkaloids are considered to be powerful catalysts for enantioselective syntheses of conformationally restricted compounds. The versatility of Cinchona alkaloids and the possibility to be easily functionalized make these commercially available catalysts to a cost-saving alternative to metal-based catalysts.

Please find further examples in the free of charge chiral catalyst data base.

(Role of Cinchona Alkaloids in the Enantio- and Diastereoselective. Synthesis of Axially Chiral Compounds, Acc. Chem. Res. 2022, 55, 24, 3551–3571; https://doi.org/10.1021/acs.accounts.2c00515).