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SN2 Reaction: Stereochemistry

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In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
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Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...

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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
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SN1 Reaction: Stereochemistry

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This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
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Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

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Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

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Squaramide-Catalyzed Asymmetric Reactions.

Bo-Liang Zhao¹, Jun-Hua Li¹, Da-Ming Du¹

¹School of Chemistry and Chemical Engineering, Beijing Institute of Technology, 5 South Zhongguancun Street, Beijing, 100081, People's Republic of China.

Chemical Record (New York, N.Y.)

|March 8, 2017

Summary

Chiral squaramides are effective hydrogen-bonding catalysts for asymmetric reactions. This review details recent advances in squaramide-catalyzed Michael, Mannich, aza-Henry, and Strecker reactions.

Keywords:

Mannich reaction Michael addition asymmetric synthesis cascade reaction hydrogen bond organocatalysis squaramides

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Area of Science:

Organic Chemistry
Catalysis
Asymmetric Synthesis

Background:

Bifunctional squaramides act as potent hydrogen-bonding catalysts.
They enable efficient asymmetric synthesis of complex molecules.
These catalysts are crucial for developing chiral compounds.

Purpose of the Study:

To review recent advancements in chiral squaramide-catalyzed asymmetric reactions.
To highlight the scope and utility of these catalysts in organic synthesis.

Main Methods:

Focuses on asymmetric Michael addition reactions.
Includes asymmetric Mannich reactions.
Covers asymmetric aza-Henry and Strecker reactions.
Discusses cascade and sequential reaction strategies.

Main Results:

Demonstrates the versatility of chiral squaramides in various asymmetric transformations.
Showcases the construction of intricate molecular architectures.
Highlights the synthesis of valuable chiral biologically active compounds.

Conclusions:

Chiral squaramide catalysis offers powerful and convenient methods for asymmetric synthesis.
These catalysts are instrumental in accessing complex chiral molecules and bioactive compounds.