Cinnoline Synthesis and Functionalization Strategies

Cinnolines are bicyclic heteroaromatic compounds formed by fusion of a benzene ring with a pyridazine ring. Their versatile scaffold has motivated the development of diverse synthetic routes, ranging from classical cyclisations of arylhydrazones to modern cross-coupling and direct C–H activation methods. Traditional protocols often rely on harsh acidic or basic conditions, whereas recent advances harness photocatalysis and electrochemical approaches to achieve milder, more sustainable transformations. Functionalisation strategies encompass halogenation, azidation, alkynylation and click-type cycloadditions, enabling fine-tuning of electronic, photophysical and biological properties. These developments have underpinned the emergence of cinnoline derivatives in medicinal chemistry, materials science and chemosensing, highlighting the global significance of efficient, selective and green synthetic methodologies.

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Cinnoline Synthesis and Functionalization Strategies publication trend

The graph below shows the total number of articles in cinnoline synthesis and functionalization strategies across all publications each year (not limited to Nature Index journals).

Technical terms

Cinnoline: bicyclic heteroaromatic scaffold comprising a benzene ring fused to a pyridazine ring.

C–H activation: direct cleavage of carbon–hydrogen bonds to enable formation of new carbon–heteroatom or carbon–carbon bonds without prefunctionalisation.

Photocatalysis: acceleration of chemical transformations through light absorption by a catalyst that facilitates bond formation or cleavage.

Azide–alkyne cycloaddition (CuAAC/SPAAC): modular ‘click’ reaction between organic azides and alkynes to yield triazole rings under catalytic or strain-promoted conditions.

Electrochemical oxidation: utilisation of controlled electrical potential to drive oxidation reactions and generate reactive intermediates for cyclisation.

References

1. Cinnoline Scaffold—A Molecular Heart of Medicinal Chemistry?. Molecules (2019).
2. Synthesis and chemosensing properties of cinnoline-containing poly(arylene ethynylene)s. Beilstein Journal of Organic Chemistry (2015).
3. Synthesis and Properties of 6-Aryl-4-azidocinnolines and 6-Aryl-4-(1,2,3-1H-triazol-1-yl)cinnolines. Molecules (2019).
4. Visible-light-assisted base-catalyzed, one-pot synthesis of highly functionalized cinnolines. Green Processing and Synthesis (2023).
5. Synthesis of Benzo[c]cinnolinium Salts from 2‑Azobiaryls by Copper(II) or Electrochemical Oxidation. Organic Letters (2024).