Secondary and primary amine catalysts for iminium catalysis

John B Brazier1, Nicholas C O Tomkinson

  • 1School of Chemistry, Main Building, Cardiff University, Park Place, Cardiff, CFIO 3AT, UK.

Summary

Iminium ion catalysis enables asymmetric cycloaddition and conjugate addition reactions. This method is practical, works in air and moisture, and offers predictive models for synthetic organic chemistry.

Related Concept Videos

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Aldehydes and Ketones with Amines: Imine Formation Mechanism

Imine formation involves the addition of carbonyl compounds to a primary amine. It begins with the generation of carbinolamine through a series of steps involving an initial nucleophilic attack and then several proton transfer reactions. The second part includes the elimination of water, as a leaving group, to give the imine.
Imines are formed under mildly acidic conditions. A pH of 4.5 is ideal for the reaction.
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Primary amines react with carbonyl compounds—aldehydes and ketones—to generate imines. Imines consist of a C=N double bond and are named Schiff bases after its discoverer—the German chemist Hugo Schiff. On the other hand, secondary amines react with carbonyl compounds to give enamines. In enamines, the presence of a C=C double bond adjacent to the nitrogen atom leads to the delocalization of the lone pair.
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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.
Preparation of 1° Amines: Azide Synthesis01:22

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Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
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Preparation of Amines: Alkylation of Ammonia and Amines01:30

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