Functional Group Migration-Driven Quaternary Carbon Editing via Intramolecular [4+2] Annulation

Area of Science:

• Organic Chemistry
• Photocatalysis
• Synthetic Methodology

Background:

• Developing efficient synthetic routes for complex heterocyclic compounds like benzo[1,6]naphthyridinones is crucial in medicinal chemistry.
• Existing methods often require harsh conditions or lack versatility for late-stage functionalization.

Purpose of the Study:

• To report a novel photocatalytic tandem radical intramolecular [4+2] cyclization for constructing functionalized benzo[1,6]naphthyridinones.
• To achieve this synthesis using unactivated cyanated alkenes under mild, metal-free conditions.

Main Methods:

• Utilizing an organic photocatalyst to initiate a radical cascade reaction.
• Employing a tandem sequence involving radical cyano migration and hydrogen atom transfer (HAT).
• Employing intramolecular [4+2] cyclization of unactivated cyanated alkenes.

Main Results:

• Successfully synthesized functionalized benzo[1,6]naphthyridinones.
• Demonstrated the feasibility of late-stage functionalization.
• Established mild reaction conditions with readily accessible substrates.
• The mechanism involves radical addition, 1,4-cyano migration, 1,6-HAT, and 6-endo-trig radical cyclization.

Conclusions:

• The developed protocol offers a new, efficient, and versatile method for synthesizing benzo[1,6]naphthyridinones.
• The metal-free, photocatalytic approach is advantageous for sustainable synthesis and late-stage functionalization.