Facilitating [2+2] Photocycloadditions by Promoting Oxygen Tolerance and Substrate Activation in Water

Abstract

Micellar photocatalysis has been used to overcome oxygen quenching and enable a [2 + 2] photocycloaddition through triplet-energy transfer in water under aerobic conditions. The cheap and commercially available self-assembling sodium dodecyl sulfate (SDS) micelles were found to increase the oxygen tolerance of a typically oxygen-sensitive reaction. Furthermore, the use of the micellar solution was found to activate α,β-unsaturated carbonyl compounds to energy transfer and allow [2 + 2] photocycloadditions to take place. Our preliminary studies of micellar effects on energytransfer-based reactions demonstrate the reaction between α,β-unsaturated carbonyl compounds and activated alkenes in a mixture of SDS, water and [Ru(bpy) 3 ](PF 6 ) 2 .[a] J.

Energy transfer photocatalysis: exciting modes of reactivity

“…This mild and easy operating method allows the synthesis of a variety of pharmaceutically relevant azetidines and oxetanes in synthetically useful yield and good selectivity. Further noteworthy advances of EnT-mediated intermolecular photocycloadditions include, for instance, the ability to use water as solvent, 84 substrate-substrate coordination, 85 and the use of photoenzymes. 86…”

Avoiding Oxygen Removal for Photochemical Reactions – towards Water as the Solvent

“…[19] Naesborg and coworkers investigated the [2 + 2] photocycloaddition of α,βunsaturated carbonyl compounds with alkenes in sodium dodecyl sulfate (SDS) micelles without the removal of oxygen. [20] In the proposed model (Figure 2), the substrates align themselves in the micelle according to their intrinsic polarity at the micelle water interface, also known as the Stern layer. The positively charged photosensitizer (Ru(bpy) 3 2 +…”

“…Noteworthy is that a variety of amphiphiles are cheap and commercially available making micellar photochemistry broadly available to the synthetic chemist [19] . Næsborg and coworkers investigated the [2+2] photocycloaddition of α,β‐unsaturated carbonyl compounds with alkenes in sodium dodecyl sulfate (SDS) micelles without the removal of oxygen [20] . In the proposed model (Figure 2), the substrates align themselves in the micelle according to their intrinsic polarity at the micelle water interface, also known as the Stern layer.…”

“…Micelle composed of sodium dodecyl sulfate (SDS) amphiphiles with a Ru(bpy) 3 2+ photosensitizer. The oxygen is proposed to be localized in the micellar core [20] …”

Surfactant-Dependent Partitioning of Organics in Aqueous–Organic Reaction Systems

“…With the high concentrations of substrates (0.1–1 M) and surfactants (1–3 wt %) employed under synthetic conditions, phase separation occurs. − Larger emulsion droplets (organic phase) contain high concentrations of organic substrates and surfactant, and likely some water; simultaneously, the aqueous phase may contain dispersed, individual micelles with organic substrates and interior water, − or free organics. The mixed composition of both phases makes the concept of phase distinction more complex.…”