A general protocol to afford enantioenriched linear homoprenylic amines

Stereoselective Synthesis of α-Disubstituted β-Homoprolines

An efficient enantioselective synthesis of chiral α-disubstituted β-homoprolines was developed, starting with the stereodivergent allylation of chiral N-tert-butanesulfinyl imines derived from 4-bromobutanal with indium or zinc and using well-established and reliable synthetic transformations. This methodology allows the easy introduction of different substituents at the α-position of the pyrrolidine scaffold and is characterized by the possibility of switching the absolute configuration of the newly formed stereocenter either by changing the configuration of the tert-butanesufinamide chiral auxiliary or by using a different stereodivergent allylation protocol with the same auxiliary.

Chiral Counteranion-Directed Catalytic Asymmetric Methylene Migration Reaction of Ene-Aldimines

A catalytic asymmetric methylene migration reaction of ene-aldimines directed by chiral counteranions is developed, with the optimal catalyst identified as phenanthryl-substituted (R)-BINOL phosphate. Control experiments and density functional theory computations reveal the importance of the 2-hydroxy group of the ene-aldimine and attractive (e.g., OH···O, CH···O, CH···π, and π···π) interactions for high enantioselectivity (up to 74% ee). The results contribute to the design of asymmetric catalysis for the rearrangement of highly reactive iminium intermediates.

HFIP-mediated 2-aza-Cope rearrangement: metal-free synthesis of α-substituted homoallylamines at ambient temperature

An efficient metal-free strategy for the synthesis of α-substituted homoallylamine derivatives has been developed via a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)-promoted 2-aza-Cope rearrangement of aldimines, generated in situ by condensation of aldehydes with easily accessible 1,1-diphenylhomoallylamines. This reaction provides rapid access to α-substituted homoallylamines with excellent functional group tolerance and yields. The reaction takes place at room temperature and no chromatographic purification is required for product isolation. The synthetic utility of the current method is further demonstrated by the transformation of the obtained benzophenone ketimines into N-unprotected homoallylamines, an α-amino alcohol and an α-amino amide.

Diastereo- and Enantioselective Synthesis of Homoallylic Amines Bearing Quaternary Carbon Centers

A Cu-catalyzed method for the efficient enantio- and diastereoselective synthesis of chiral homoallylic amines bearing a quaternary carbon and an alkenylboron is disclosed. Transformations are promoted by a readily prepared (phosphoramidite)-Cu complex and involve bench-stable γ,γ-disubstituted allyldiborons and benzyl imines; products are obtained in up to 82% yield, >20:1 dr, and >99:1 er. Reactions proceed via stereodefined boron-stabilized allylic Cu species formed by an enantioselective transmetalation. Utility of the 1-amino-3-alkenylboronate products is highlighted by a variety of synthetic transformations.

Brønsted Acid-Initiated Formal [1,3]-Rearrangement Dictated by β-Substituted Ene-Aldimines

The rearrangement of ene-aldimines is a useful reaction for affording homoallylic amines. Despite their utilities in synthetic chemistry, the rearrangement for accessing homoallylic amines substituted at the 2-position remains elusive. In this study, the Brønsted acid-initiated formal [1,3]-rearrangement of ene-aldimines was developed to synthesize 2,4,4-substituted homoallylic amines that were otherwise inaccessible previously. Our study reveals an intermolecular pathway in which the rearrangement proceeds via a protonation-mediated 2-azaallenium cation.

Lewis acidic FeCl3 promoted 2-aza-Cope rearrangement to afford α-substituted homoallylamines in dimethyl carbonate

The current work shows an iron-catalyzed 2-aza-Cope rearrangement in dimethyl carbonate for the synthesis of a wide variety of α-substituted homoallylamines from readily accessible starting materials with diverse functional groups.