General and Efficient Intermolecular [2+2] Photodimerization of Chalcones and Cinnamic Acid Derivatives in Solution through Visible‐Light Catalysis

Abstract

[2+2] Photocycloaddition, for example, the dimerization of chalcones and cinnamic acid derivatives, is a unique strategy to construct cyclobutanes, which are building blocks for a variety of biologically active molecules and natural products. However, most attempts at the above [2+2] addition have focused on solid-state, molten-state, or host-guest systems under ultraviolet-light irradiation in order to overcome the competition of facile geometric isomerization of nonrigid olefins. We report a general and simple method to realize the intermolecular [2+2] dimerization reaction of these acyclic olefins to construct cyclobutanes in a highly regio- and diastereoselective manner in solution under visible light, which provides an efficient solution to a long-standing problem.

Enantioselective [2+2] Photocycloaddition Reactions of Enones and Olefins with Visible Light Mediated by N,N′‐Dioxide–Metal Complexes

“…With the releaseo f the optically active cyclobutane 3a,t he catalyst is regenerated and participates in the next catalytic cycle. In addition, due to the high reactivity of intermediate III,o ther competitive pathways, including the regioselective [2+ +2] cycloaddition reaction with alkene 2a and the homodimerization of 1a, [27] may occur leadingtos everalbyproducts (shown in Scheme 2).…”

Cage-confined photocatalysis for wide-scope unusually selective [2 + 2] cycloaddition through visible-light triplet sensitization

“…However, geometric isomerization and racemic background photoreactions facilely induced by UV light make the stereochemical control of cycloaddition a long-standing challenge, especially for acyclic alkenes 8,9 . As a green and clean procedure for chemical process and production that are contemporarily demanded by sustainable development, the visible-light sensitized intra-and intermolecular [2 + 2] cycloaddition of olefins has drawn great attention of chemical society in past decades [10][11][12][13][14][15] , leading to fast progress in [2 + 2] photocycloaddition of nonrigid olefins with excellent regio-and stereoselectivities [16][17][18][19][20] . Nevertheless, owing to steric preference and relative radical stability of excited-state intermediates, hitherto, the stereochemical control is mainly achieved for the thermodynamic favored anti-diastereomers from acyclic olefins, e.g., styrenes, chalcones, and cinnamates 16,[21][22][23][24] .…”

Visible light-mediated intermolecular [2 + 2] photocycloaddition of 1-aryl-2-nitroethenes and olefins

“…Although the nitro chromophore bears electronically some analogy to a carbonyl group, the photochemical behaviour of 1-phenyl-2-nitroethene is different from cinnamic aldehyde. While the latter compound does not form cyclobutanes upon direct irradiation 36 the former compound and its analogues are suitable substrates for [2 + 2] photocycloaddition reactions, as shown in this study. For 1-aryl-2-nitroethenes, an intrinsic feature of their excited state seems to be the propensity to react only with electron rich olefins.…”