Research

H.-F. Li, W. Cao, X. Ma, X. Xie, Y. Xia and Z. Ouyang; "Visible-Light-Driven [2 + 2] Photocycloadditions between Benzophenone and C=C Bonds in Unsaturated Lipids", Journal of the American Chemical Society,2020, 142, 3499-3505

https://doi.org/10.1021/jacs.9b12120

The [2 + 2] photocycloaddition of alkenes and carbonyls is of fundamental interest and practical importance, as this process is extensively involved in oxetane-ring constructions. While individual carbonyl group or alkene moiety has beenutilized as photoactive species for oxetane formations upon ultraviolet photoexcitation, direct excitation of the entire non-covalent complex involving alkene and carbonyl substrates to achieve [2 + 2] photocycloadditions is rarely addressed.Herein, complexes with non-covalent interactions between benzophenone and C=C bonds in unsaturated lipids have been successfully characterized and for the first time a [2 + 2] cycloaddition leading to the formation of oxetanes has been identified under visible-light irradiation. The mechanism of this reaction is distinctly different from the well-studied Paternò−Büchi reaction. The entire complexes characterized as dimeric proton-bonded alkene and carbonyl substrates can be excited under visible light, leading to electron transfer from the alkene moiety in fatty acyls to the carbonyl group within the complex. These results provide a new insight into utilizing non-covalent complexes for the synthesis of oxetanes, in which the excitation wavelength becomes independent of each individual substrate.