Intermolecular [2π+2σ]-photocycloaddition enabled by triplet energy transfer

Area of Science:

• Organic Chemistry
• Photochemistry
• Synthetic Methodology

Background:

• Photochemical [2+2]-cycloadditions traditionally involve two π-electron systems to form cyclobutanes.
• Existing methods predominantly focus on [2π+2π]-cycloadditions, converting two π-bonds into two new C-C σ-bonds.
• Access to bicyclo[2.1.1]hexanes, important in pharmaceutical research as bioisosteres, is limited.

Purpose of the Study:

• To report a novel intermolecular [2+2]-photocycloaddition reaction.
• To utilize bicyclo[1.1.0]butanes as 2σ-electron reactants.
• To develop a new synthetic route to bicyclo[2.1.1]hexanes.

Main Methods:

• Employing visible-light-mediated triplet energy transfer catalysis.
• Utilizing bicyclo[1.1.0]butanes as σ-bond synthons in a [2π+2σ]-photocycloaddition.
• Coupling heterocyclic olefins such as coumarins, flavones, and indoles.

Main Results:

• Demonstration of an intermolecular [2+2]-photocycloaddition involving σ-bonds.
• Development of a simple, modular, and diastereoselective synthesis of bicyclo[2.1.1]hexanes.
• Generation of previously inaccessible structural motifs.

Conclusions:

• The developed strategy successfully extends intermolecular [2+2]-photocycloadditions to σ-bonds.
• This method provides a valuable new approach for synthesizing bicyclo[2.1.1]hexane scaffolds.
• The reaction offers access to novel molecular architectures relevant to medicinal chemistry.