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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

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Published on: June 21, 2017

Asymmetric Reductive Cross-Coupling of Aldimines

Yuhao Dai¹, Fang Fang², Guangqing Xu³

¹School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.

Organic Letters

|April 27, 2026

Abstract:

Unsymmetrical chiral 1,2-diamines are important motifs widely present in pharmaceuticals, chiral auxiliaries, and ligands/catalysts. A novel and efficient strategy for the modular synthesis of unsymmetrical chiral 1,2-diaryl ethylenediamines via chiral diboron-templated reductive cross-coupling of aldimines has been established. By leveraging both steric and concentration effects, good chemoselectivity and enantioselectivity have been achieved and homocoupling side-reactions are effectively inhibited. The method exhibits good functional group tolerance and scalability, offering a practical and versatile route to unsymmetrical chiral 1,2-diamines.

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Crossed Aldol Reactions: Overview

Crossed Aldol Reactions: Overview

Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds function as nucleophiles and electrophiles. As shown in Figure 1, such a reaction yields a mixture of products, two of which are formed via self-condensation, while the remaining two are formed via crossed-condensation. Without adjustment, the reaction's usefulness in organic chemistry is decreased.

Preparation of Amines: Reductive Amination of Aldehydes and Ketones

Preparation of Amines: Reductive Amination of Aldehydes and Ketones

Carbonyl compounds and primary amines undergo reductive amination first to produce imines, followed by secondary amines in the same reaction mixture, using selective reducing agents like sodium cyanoborohydride or sodium triacetoxyborohydride. Reductive amination produces different degrees of substitution of amines depending on the starting amine substrate.

Amides to Amines: LiAlH4 Reduction

Amides to Amines: LiAlH₄ Reduction

Amide reduction with strong reducing agents like lithium aluminum hydride proceeds through a nucleophilic acyl substitution to form amines. Primary, secondary, and tertiary amides yield primary, secondary, and tertiary amines, respectively.
Amide reduction requires two equivalents of the reducing agent, acting as a source of hydride ions. As shown in the figure, the reaction is initiated with a nucleophilic attack by the hydride ion at the carbonyl carbon to form a tetrahedral intermediate.

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.

Crossed Aldol Reaction Using Weak Bases

Crossed Aldol Reaction Using Weak Bases

This lesson deals with the crossed aldol reaction using weak bases. The self-condensation of an aldehyde having α hydrogen is prevented by adding it slowly to a mixture of formaldehyde and weak bases like hydroxide and alkoxide. Upon slow addition of the aldehyde, the base deprotonates the α carbon of the aldehyde to form the corresponding enolate. The enolate subsequently attacks the formaldehyde to form a single crossed product. Figure 1 depicts the aforementioned reaction.

Crossed Aldol Reaction Using Strong Bases: Directed Aldol Reaction

Crossed Aldol Reaction Using Strong Bases: Directed Aldol Reaction

The reaction between two different carbonyl compounds comprising α hydrogen in the presence of a strong base like lithium diisopropylamide (LDA) to form a crossed aldol product is known as a directed aldol reaction. The directed aldol reaction is depicted in Figure 1.

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