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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Cation-pi controlled solid-state photodimerization of 4-azachalcones
1Department of Chemistry, Faculty of Science, Ochanomizu University, Bunkyo-ku, Tokyo 112-8610, Japan.
This study introduces cation-pi interactions to control solid-state photodimerization of alkenes. This method enhances stereoselective cyclobutane dimer formation, offering a novel approach for alkene transformations.
Area of Science:
- Organic Chemistry
- Photochemistry
- Crystallography
Background:
- Solid-state photodimerization offers a pathway to stereoselective synthesis.
- Controlling molecular alignment in crystals is crucial for efficient solid-state reactions.
- Cation-pi interactions are increasingly recognized for their role in molecular recognition and self-assembly.
Purpose of the Study:
- To investigate the use of cation-pi interactions for controlling alkene alignment in solid-state photodimerization.
- To explore the stereoselective formation of cyclobutane dimers via this novel approach.
- To demonstrate the effectiveness of pyridinium-aromatic cation-pi interactions in directing photodimerization.
Main Methods:
- Synthesis and characterization of azachalcone derivatives and their hydrochloride salts.
- Solid-state photodimerization experiments upon UV irradiation.
- X-ray crystallographic analysis to determine crystal structures and intermolecular interactions.
- Comparative analysis of crystal packing structures to elucidate the role of cation-pi interactions.
Main Results:
- Photodimerization of 4-azachalcone (1a) yielded the synHT dimer 2a (49% yield).
- Photodimerization of 4'-methoxy-4-azachalcone (1b) yielded the synHH dimer 3b (67% yield).
- Photodimerization of hydrochloride salts (1a.HCl and 1b.HCl) exclusively afforded synHT dimers (2a and 2b) in quantitative yields.
- X-ray crystallography revealed significantly shorter reactive double bond separations in HCl salts due to intermolecular cation-pi interactions.
Conclusions:
- Intermolecular cation-pi interactions in pyridinium salts effectively control alkene alignment in the solid state.
- This approach significantly enhances the stereoselectivity of cyclobutane dimer formation.
- Cation-pi controlled solid-state photodimerization is a powerful strategy for synthesizing cyclobutane dimers.
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