Crossed Intermolecular [2+2] Cycloadditions of Acyclic Enones via Visible Light Photocatalysis

Abstract

Efficient [2+2] heterodimerizations of dissimilar acyclic enones can be accomplished upon visible light irradiation in the presence of a ruthenium(II) photocatalyst. Similar cycloadditions under standard UV photolysis conditions are inefficient and unselective. Nevertheless, a diverse range of unsymmetrical tri- and tetrasubstituted cyclobutane structures can be produced in good yields and excellent diastereoselectivities using this new method. The reaction is promoted by any visible light source, and efficient, gram-scale cycloadditions can be conducted upon irradiating with ambient sunlight.

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

“…These experiments revealed an increase in k obs associated with an increase in [ Building upon these early observations that Brønsted acids can play a significant role in catalyzing electron transfers, Yoon and coworkers reported an acid-catalyzed reductive cyclization of enones in the context of visible light photoredox catalysis ( Figure 46) [253]. The Yoon lab had previously demonstrated the ability of Lewis acid salts to activate similar systems [254][255], however different products were formed based on the method of enone activation. Specifically, it was proposed that Lewis acid activation affords a radical anion intermediate, whereas Brønsted acid activation results in a neutral radical.…”

Photoredox catalysis by [Ru(bpy)3]2+ to trigger transformations of organic molecules. Organic synthesis using visible-light photocatalysis and its 20th century roots

“…Here, C 2 symmetric products such as 96 were produced, which was in contrast to the tethered intramolecular reactions. In a related work, challenging crossed intermolecular [2+2] cycloaddition of two different enones was accomplished (Scheme 40) 57 . With this method, a diverse range of non-symmetric tri-and tetrasubstituted cyclobutane structures was produced in good yields and diastereoselectivities (Scheme 41).…”

Photoredox Catalysis with Visible Light

“…[16] While higher-energy UV light can be directly absorbed by acyclic enones, it causes predominately photochemical E/Z isomerization of the substrates. [17] In contrast, the photocatalyzed reaction proceeds considerably differently.…”