Chiral amines in the asymmetric synthesis of axially chiral allenes through catalysis and covalent chirality transfer

Abstract

Axially chiral allenes are useful motifs and intermediates in stereoselective synthesis. Chiral amines provide several routes to these structures, but their operational roles differ. An amine may act as a regenerated organocatalyst, cooperate with a metal catalyst, or serve as a stoichiometric covalent mediator that transfers stereochemical information through a propargylamine. This review compares these roles using amine loading, substrate activation, stereochemical evidence and regeneration as organizing criteria. Noncovalent additions, isomerizations and proton-transfer reactions are considered alongside enamine and dienamine catalysis, stereoselective functionalization of pre-existing allenes, and cooperative palladium-amine and gold-squaramide chemistry. Metal-assisted rearrangements of chiral propargylamines provide complementary access to allenes through covalent chirality transfer. Quantitative examples distinguish matched yields and selectivities from scope maxima, and separate reaction performance from mediator recovery after chemical reduction. The literature demonstrates both catalytic axis construction and catalytic control of axial and central stereochemistry. A remaining challenge is to extend amine turnover to broadly modular alkyne-carbonyl-propargylamine sequences while closing the hydrogen-transfer and regeneration balance. Progress will require substrate-specific mechanistic evidence, reproducible stereochemical analysis and quantitative assessment of temperature, scale and reagent demand.

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