Re-Inventing Olefin Oxidation Using Visible-Light Photocatalysis

Olefins are feedstocks readily available from petroleum and vegetable biomass with an integral role in the preparation of high-value materials. In particular, oxidation reactions are used to introduce oxygen atoms across the olefin carbons and thus convert these molecules into a broad spectrum of synthetic intermediates like aldehydes, ketones, alcohols and carboxylic acids.

Olefin oxidation is generally performed using the ozonolysis reaction which is mostly adopted by the bulk chemical industry where safe and large-scale processes on structurally simple materials are possible. The fine chemical sector (pharmaceutical and agrochemical industries) do not use this reactivity as their substrates are complex and contain fragile functionalities. This means that multi-step approaches are still required to overcome this synthetic challenge. The invention of a new chemical strategy able to achieve the general and selective oxidation of olefin building blocks is of strategic importance to facilitate and streamline the identification and the preparation of molecules critical to our society.

The overarching aim of this proposal is to develop the first example of a visible-light-mediated photochemical reaction enabling the oxidative cleavage of olefin building blocks to produce aldehydes and ketones. In this way, we will provide a unique reaction able to streamline the synthesis O-containing fragments currently difficult to prepare but highly sought after by pharmaceutical and agrochemical discovery programs.

- We aim to use simple nitro-aromatics, a large class of feedstocks produced annually on multi ton-scale, as photoactive oxidants in combination with visible-light and a photocatalyst. This strategy will explore the ability of nitro-arenes to undergo photoexcitation to their triplet state by direct energy-transfer. These species will then engage in novel radical [3+2]-type cycloadditions with olefins to give a new class of heterocycles. The species formed by this reaction can be effectively considered as N-doped ozonides and will undergo fast cleavage across the C-C bond thus leading to the oxidised materials.

- We will run detailed mechanistic studies to fully understand the activation process as well as the reactivity of triple nitro-arenes.

- We will then benchmarke this reactivity to achieve the oxidation of progressively more complex and functionalised olefin building blocks. We aim to prepare a large library of nitro-aromatics to evaluate heir triplet state reactivity. This might enable the identification of reagents able to selectively discriminate between olefins based on steric or electronic factors.

Overall, this project will develop an innovative strategy for the fast, selective and mild oxidation of olefins. The possibility to access these high-value materials will facilitate the discovery, development and manufacture of therapeutic agents and agrochemicals with overall impact to the well-being of UK society.