Kai Rossen

Applying green chemistry to the photochemical route to artemisinin

Artemisinin is an important antimalarial drug, but, at present, the environmental and economic costs of its semi-synthetic production are relatively high. Most of these costs lie in the final chemical steps, which follow a complex acid- and photo-catalysed route with oxygenation by both singlet and triplet oxygen. We demonstrate that applying the principles of green chemistry can lead to innovative strategies that avoid many of the problems in current photochemical processes. The first strategy combines the use of liquid CO2 as solvent and a dual-function solid acid/photocatalyst. The second strategy is an ambient-temperature reaction in aqueous mixtures of organic solvents, where the only inputs are dihydroartemisinic acid, O2 and light, and the output is pure, crystalline artemisinin. Everything else-solvents, photocatalyst and aqueous acid-can be recycled. Some aspects developed here through green chemistry are likely to have wider application in photochemistry and other reactions.

Photocatalytic hydroxylation of arylboronic acids using continuous flow reactors

The photocatalytic oxidation of mono- and di-substituted arylboronic acids to phenols has been investigated using a continuous flow photoreactor fitted with white LEDs. An EtOH–H2O solvent system accelerated conversion at 2 MPa; whereas reactions at atmospheric pressure allowed for moderately efficient desymmetrisation.