Organocatalytic Aza-Michael Addition Chemistry

Organocatalytic aza-Michael addition represents the conjugate addition of amines or related nitrogen nucleophiles to electron-deficient olefins under the influence of small organic molecules. In contrast to traditional metal-based catalysts, organocatalysts such as secondary amines, cinchona alkaloid derivatives, squaramides and N-heterocyclic carbenes promote carbon–nitrogen bond formation via non-covalent hydrogen bonding or transient covalent activation. This strategy offers mild reaction conditions, operational simplicity and compatibility with a wide variety of functional groups. The method has been harnessed to assemble diverse nitrogen-containing scaffolds, including chiral β-amino acids, heterocyclic building blocks and peptidomimetic fragments, often with high enantioselectivity. Key mechanistic pathways involve either iminium-enamine activation, wherein the catalyst forms an iminium ion with the Michael acceptor to increase electrophilicity, or bifunctional activation, in which hydrogen-bond donors orient both nucleophile and electrophile. Recent efforts have focused on expanding substrate scope to include unactivated amides and lactams, enhancing stereocontrol through novel chiral frameworks and integrating aza-Michael addition into cascade processes. The approach aligns with the principles of green chemistry by avoiding heavy metals and minimising waste, and finds application in the synthesis of pharmaceuticals, agrochemicals and advanced materials.

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Organocatalytic Aza-Michael Addition Chemistry publication trend

The graph below shows the total number of articles in organocatalytic aza-michael addition chemistry across all publications each year (not limited to Nature Index journals).

Technical terms

Organocatalysis: Catalysis by small organic molecules lacking metals, relying on hydrogen bonding or covalent activation to accelerate reactions.

Aza-Michael Addition: Conjugate addition of an amine (or related nitrogen nucleophile) to an α,β-unsaturated carbonyl compound, forming a new C–N bond.

Michael Acceptor: An electron-deficient alkene or alkyne, typically bearing an electron-withdrawing group, that undergoes conjugate addition.

Enantioselectivity: Preference for the formation of one enantiomer over the other in a chiral chemical reaction, often expressed as enantiomeric excess.

Bifunctional Catalyst: A catalyst possessing two distinct activation sites (for example, a hydrogen-bond donor and a basic amine) that simultaneously orient nucleophile and electrophile to enhance reactivity and selectivity.

References

1. Synthesis of New Azetidine and Oxetane Amino Acid Derivatives through Aza-Michael Addition of NH-Heterocycles with Methyl 2-(Azetidin- or Oxetan-3-Ylidene)Acetates. Molecules (2023).
2. Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides. Beilstein Journal of Organic Chemistry (2021).
3. Green synthesis of new acyl hydrazide derivatives by single and double aza-Michael reaction under solvent-free conditions. Green Chemistry Letters and Reviews (2017).