Axially chiral biphenyls as scaffolds for frustrated Lewis pairs

Frustrated Lewis Pairs (FLPs) are an inter- or intramolecular combination of a Lewis acid and a Lewis base, sterically or geometrically prevented from forming the classical Lewis acid−base adduct. Thus, Lewis acidity and... [ view full abstract ]

Frustrated Lewis Pairs (FLPs) are an inter- or intramolecular combination of a Lewis acid and a Lewis base, sterically or geometrically prevented from forming the classical Lewis acid−base adduct. Thus, Lewis acidity and basicity of both partners are still available for interaction with a third molecule (Scheme 1). In the past decade, this notion has emerged as a general strategy that enables main-group compounds to activate small molecules like H₂, CO₂ or silanes. Numerous FLP catalysts are now able to effect various chemical transformations of interest for synthetic organic chemistry.^[1]

Despite this growing interest, asymmetric applications of FLP catalysts have been limited so far to the reduction of unsaturated systems; furthermore the modularity of catalysts has still to be improved.^[2-4] Our current work concerns the synthesis of Lewis acids and bases based on the axially chiral biphenyl scaffold.^[5] Unlike the parent axially chiral binaphthyl backbone, this unexplored scaffold in FLP chemistry allows more variations of structural and electronic parameters (Scheme 2). We will detail our efforts towards atropo-enantiopure biphenyl-phosphines and –boranes and their application in catalysis.

References:

[1] D. W. Stephan, G. Erker, Angew. Chem. Int. Ed. 2015, 54, 6400.

[2] D. W. Stephan, J. Am. Chem. Soc. 2015, 137, 10018.

[3] X. Feng, H. Du, Tetrahedron Lett. 2014, 55, 6959.

[4] L. Shi, Y.-G. Zhou, ChemCatChem 2015, 7, 54.

[5] M. J. Fer, J. Cinqualbre, J. Bortoluzzi, M. Chesse, F. R. Leroux, A. Panossian, Eur. J. Org. Chem. 2016, 4545.