Cover Feature: Facilitating [2+2] Photocycloadditions by Promoting Oxygen Tolerance and Substrate Activation in Water (Chem. Eur. J. 26/2023)

Abstract

Micellar photocatalysis allows for a simple and benign reaction set‐up using water as the solvent without the need for oxygen‐removing protocols. Blue light (456 nm) is absorbed by the photocatalyst and allows the [2+2] photocycloaddition to occur between α,β‐unsaturated carbonyl compounds and activated alkenes. The observed reactivity for α,β‐unsaturated aldehydes is completely turned on by the use of a micellar solution as opposed to organic solvents. More information can be found in the Research Article by L. Næsborg and co‐workers (DOI: 10.1002/chem.202300627).

Photocyclization by a triplet–triplet annihilation upconversion pair in water – avoiding UV-light and oxygen removal

“…Using an aqueous sodium dodecyl sulfate (SDS) solution under green-light irradiation led to the desired ketone 2a in 62% NMR yield (Table 1, entry 1). Previous work from our group 25 showed that an oxygen sensitive photocycloaddition promoted by [Ru(bpy) 3 ] 2+ , which has been used as an oxygen sensor, 26 could be performed in micellar media without freeze-pump-thaw protocols. We hoped to observe similar effects in our protocol for a highly oxygen sensitive TTA-UC process, 27 and did not make any efforts to remove oxygen.…”

Solvent Dependency of Catalyst‐Substrate Aggregation Through π‐π Stacking in Photoredox Catalysis

“…This further substantiates the idea that preassemblies form prior to oxidation, which are then bound more tightly upon oxidation which then alters the UV-vis and allows a catalytic reaction to take place. Such a finding reveals the critical role that solvents play in influencing outcomes of PRC reactions even in homogeneous solutions and not only micellular dispersions [25][26][27] and demands that solvent molecules are treated in experiments and calculations as an additional variable capable of tuning and not just as a spectator to the PRC reaction. Finally, our study highlights the added value of MD calculations in unravelling the mechanisms of PRC reactions that complements other theoretical approaches (QC) [28] and experimental approaches like isolation of authentic redox states.…”