Progress on the Enantioselective Synthesis of Axially Chiral Cycloalkylidenes

Abstract

The discovery of new asymmetric synthetic methodologies and the asymmetric synthesis of new chiral compounds have been the central work of synthetic organic chemists for decades. Axially chiral compounds have gained considerable attention in recent years because of their unique utility in asymmetric catalysis and synthesis. The asymmetric synthesis of axially chiral cycloalkylidenes, a subset of axial chirality molecules, is sluggish compared to chiral allenes, and chiral biaryl compounds. In this review, different approaches for the synthesis of axially chiral cycloalkylidenes are summarized.

Enantioselective Potassium-Catalyzed Wittig Olefinations

“…The Wittig reaction has stood as one of the essential methods for stereoselective alkene synthesis since its initial report, , finding continuous application in both industry and academia to this day. − Olefination of suitably substituted prochiral ketones permits the formation of axially chiral alkene products, − and numerous approaches to asymmetric Wittig and Horner–Wadsworth–Emmons reactions have been demonstrated using stoichiometric chiral controlling elements, with canonical examples relying on covalent chiral auxiliaries − or chiral ligands. , In contrast, examples of asymmetric catalysis of Wittig-type olefinations to access axially chiral products are exceedingly rare; to our knowledge there exist only three reported examples, using either Brønsted acid, H-bond-donor, or phase-transfer catalysts and attaining up to 75% enantiomeric excess (ee) (Scheme A). − Herein we report highly enantioselective Wittig reactions of 4-substituted cyclohexanones catalyzed by a novel potassium–isothiourea–boronate complex.…”