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Development of Photochemical Strategies for the Generation and Use of Sulfur Radicals in the Assembly of C-S Bonds

Periodic Reporting for period 1 - LOBSTER (Development of Photochemical Strategies for the Generation and Use of Sulfur Radicals in the Assembly of C-S Bonds)

Reporting period: 2019-05-01 to 2021-04-30

• What is the problem/issue being addressed?
This Fellowship aimed at delivering transformative advances towards the assembly of sulfur-containing molecules of interest to the pharmaceutical and agrochemical industry sectors. The project was based on the use of visible-light as the source of energy for the generation and use of sulfur radicals in organic synthesis. The main aspect was the design of a novel class of derivatives able to undergo single electron transfer with photoexcited catalyst and then lead to S–O bond fragmentation as blueprint for S-radical formation.

• Why is it important for society?
This project aims at delivering fundamental advances for the preparation of sulfur-containing molecules (thioether, sulfones, sulfonamides...) which are fundamental to the discovery and evolution of drugs, agrochemicals and food additives. Improving the way we make these molecules underpins the manufacture of high-value materials that impact positively our lives.

• What are the overall objectives?
1) Develop a novel class of derivatives based on the presence of weak S–O bonds that could be activated by visible-light irradiation
2) Develop novel divergent and multicomponent processes cyclization of sulfur radicals
3) Use sulfur radicals for the intriduction of S-functionalities onto aromatics
• We started our work preparing a series of derivatives based on the presence of a weak O–S bond. These compounds were all characterized spectroscopically and electrochemically.
• We realised that their reduction was reversible and that upon SET they would not undergo S–O bond cleavage.
• During the attempts to explore their reactivity under photoredox catalysis we discovered that amines, another class of fundamental building blocks were undergoing demethylation reactions.
• Since this type of reactivity was unkown, we explored it at a full extent.
• This work has been published in the peer-reviewed journal Angew. Chem. Int. Ed. 2021, 60, 7669-7674.
• We then further expanded this reactivity to have modify in a different way S-containing molecules and introduce selectively olefin functionalities into their structures.
• • This work has been published in the peer-reviewed journal J. Am. Chem. Soc. 2021, 143, 14806-14813
• The results obtained in this Fellowship have demonstrated a fundamentally novel method to functionalise amines and sulfur-containing molecules using photoredox catalysis.