Stereocontrol via Propeller Chirality in FLP-Catalyzed Asymmetric Hydrogenation

18 January 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Utilization of chiral frustrated Lewis pairs as catalysts in enantioselective hydrogenation of unsaturated molecules represents a promising approach in asymmetric synthesis. In our effort to improve our current understanding of the factors governing the stereoselectivity in these catalytic processes, herein we examined the mechanism of direct hydrogenation of aromatic enamines catalyzed by a binaphthyl-based chiral amino-borane. Our computational analysis reveals that only one particular conformer of the key borohydride reaction intermediate can be regarded as a reactive form of this species. This borohydride conformer has a well-defined chiral propeller shape, which induces facial selectivity in the hydride transfer to pro-chiral iminium intermediates. The propeller chirality of the reactive borohydride conformer is generated by the axially chiral binaphthyl scaffold of the amino-borane catalyst through stabilizing pi-pi stacking interactions. This new computational insight can be readily used to interpret the high degree of stereoinduction observed for these reactions. We expect that the concept of chirality relay could be further exploited in catalyst design endeavors.


asymmetric hydrogenation
frustrated Lewis pairs
chirality relay

Supplementary materials

ESI: Stereocontrol via Propeller Chirality in FLP-Catalyzed Asymmetric Hydrogenation
Details regarding the computational analysis, total energies and Cartesian coordinates for the considered stationary points


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