Lawesson's Reagent: Providing a New Approach to the Forgotten 6-Thioverdazyl Radical

Area of Science:

• Organic Chemistry
• Radical Chemistry

Background:

• 1,5-dimethyl-6-thioverdazyl radicals are underrepresented in chemical literature.
• Efficient synthesis methods for these radicals are lacking.

Purpose of the Study:

• To develop a novel and scalable method for preparing 1,5-dimethyl-6-thioverdazyl radicals.
• To investigate the factors influencing the synthesis efficiency.
• To characterize the electronic and redox properties of the synthesized radicals.

Main Methods:

• Employing Lawesson's reagent for direct thionation of dialkylbishydrazone precursors.
• Utilizing cyclization to form the tetrazinanthione verdazyl precursor.
• Oxidation to yield the final 6-thioverdazyl radical.
• Density functional theory (DFT) for mechanistic insights.
• Electron paramagnetic resonance (EPR) for electronic characterization.

Main Results:

• Successful gram-scale preparation of 1,5-dimethyl-6-thioverdazyl radicals.
• High thionation yields observed for substrates with electron-withdrawing groups.
• Reduced yields for parent phenyl or electron-donating substituted substrates.
• A one-pot synthesis strategy developed using in situ cyclization to improve efficiency.
• Characterization of radical electronic nature and first report of redox properties.

Conclusions:

• A robust and scalable synthetic route to 1,5-dimethyl-6-thioverdazyl radicals has been established.
• The synthetic efficiency is influenced by the electronic nature of substituents on the precursor.
• This work provides valuable data on the electronic and redox behavior of 6-thioverdazyl radicals.