Modular Synthesis of Enantioenriched α-Chiral Homoallylic Amidines Enabled by Relay Ir/Cu Catalysis

The cascade of Ir-catalyzed enantioselective allylic amination and Cu-catalyzed alkyne-azide cycloaddition was designed for the asymmetric synthesis of homoallylic amidines. The nucleophilic addition of an in situ-generated enantioenriched tertiary allylamine to a ketenimine intermediate triggers a rapid and stereospecific zwitterionic aza-Claisen rearrangement in a 1,3-chiral transfer manner. The approach allows modular access to enantioenriched α-chiral homoallylic amidines in high yields with a high level of enantiomeric purity.

Asymmetric Aza-Claisen Rearrangement between Enantioenriched α-Chiral Allylamines and Allenones

An unprecedented asymmetric aza-Claisen rearrangement between enantioenriched α-chiral allylamines and allenones was found to proceed in the absence of catalysts and additives at room temperature. The rearrangement, followed by hydrolysis, provides convenient access to structurally diverse δ-chiral β-diketones in good to excellent yields with excellent retention of enantiopurity. This protocol proved powerful for the construction of an all-carbon quaternary stereocenter with high enantiopurity.

Enantioselective Allenoate-Claisen Rearrangement Using Chiral Phosphate Catalysts

Herein we report the first highly enantioselective allenoate-Claisen rearrangement using doubly axially chiral phosphate sodium salts as catalysts. This synthetic method provides access to β-amino acid derivatives with vicinal stereocenters in up to 95% ee. We also investigated the mechanism of enantioinduction by transition state (TS) computations with DFT as well as statistical modeling of the relationship between selectivity and the molecular features of both the catalyst and substrate. The mutual interactions of charge-separated regions in both the zwitterionic intermediate generated by reaction of an amine to the allenoate and the Na⁺-salt of the chiral phosphate leads to an orientation of the TS in the catalytic pocket that maximizes favorable noncovalent interactions. Crucial arene-arene interactions at the periphery of the catalyst lead to a differentiation of the TS diastereomers. These interactions were interrogated using DFT calculations and validated through statistical modeling of parameters describing noncovalent interactions.