Light-Induced SO Extrusion from Tribenzothiepine S-oxides: A Precursor Approach to the Triphenylene Core

Area of Science:

• Organic Chemistry
• Materials Science
• Photochemistry

Background:

• The precursor approach enables synthesis of insoluble/unstable polycyclic aromatic hydrocarbons (PAHs).
• Current methods using retrocycloaddition and decarbonylation limit structural diversity.
• New reactivity schemes are crucial for expanding the precursor approach.

Purpose of the Study:

• To investigate the tribenzo[b,d,f]thiepine S-oxide as a photoactivatable precursor for triphenylene.
• To explore new photochemical transformations for the precursor approach.
• To develop a green route for triphenylene synthesis.

Main Methods:

• Chemo- and stereoselective synthesis of tribenzothiepine S-oxide isomers using mCPBA and a boron-based Lewis acid.
• Spectroscopic analyses and DFT-based mechanistic studies.
• UV light irradiation of isomers in solution and solid state.

Main Results:

• Stable exo and endo isomers of tribenzothiepine S-oxide were synthesized.
• Stereodependent photochemical behavior was observed.
• UV irradiation converted exo-isomer to triphenylene with up to 90% yield via SO extrusion.
• Endo isomer photoisomerized to exo isomer before SO extrusion.
• Solid-state photoconversion demonstrated potential for post-processing.

Conclusions:

• Tribenzo[b,d,f]thiepine S-oxide serves as an effective photoactivatable precursor for triphenylene.
• The stereochemistry of the isomers dictates their photochemical fate.
• This work expands the precursor approach with a novel SO extrusion pathway.
• Cyclic sulfoxides offer potential for green, solid-state synthesis of triphenylene-based materials.