Direct Access to Cinnoline-4-carbaldehydes: Iridium(III)-Catalyzed C-H [4 + 2] Annulation Using 2-Chloromalonaldehyde...

Area of Science:

• Organic Chemistry
• Catalysis
• Heterocyclic Chemistry

Background:

• Cinnolines are an important class of nitrogen-containing heterocycles with diverse biological activities.
• Existing synthetic routes to cinnoline derivatives can be complex and lack efficiency.
• Development of novel synthetic methodologies for accessing functionalized cinnolines is crucial.

Purpose of the Study:

• To develop a concise and efficient synthesis of diazaheterocycle-fused cinnolines.
• To explore the utility of 2-chloromalonaldehyde as a C2 synthon in metal-catalyzed reactions.
• To introduce a versatile aldehyde group for subsequent functionalization of cinnoline derivatives.

Main Methods:

• Iridium(III)-catalyzed [4 + 2] annulation reaction.
• Utilized 1-aryl-1,2-dihydropyridazine-3,6-diones and 2-chloromalonaldehyde as starting materials.
• Employed a dephthaloylation step to yield the final products.

Main Results:

• Achieved a concise synthesis of diazaheterocycle-fused cinnolines.
• Successfully employed 2-chloromalonaldehyde as a C2 synthon for the first time in metal-catalyzed cyclizations.
• Efficiently installed an aldehyde group, enabling further synthetic transformations.
• Obtained valuable cinnoline-4-carbaldehyde derivatives.

Conclusions:

• The developed Ir(III)-catalyzed annulation provides a novel and efficient route to cinnoline derivatives.
• The use of 2-chloromalonaldehyde expands the scope of synthons in metal-catalyzed cyclizations.
• The resulting cinnoline-4-carbaldehydes are versatile intermediates for further chemical synthesis.