Abstract
An efficient, concise, and green visible-light-mediated [2 + 2] cycloaddition reaction for the diastereoselective synthesis of dihydrocyclobuta[b]naphthalene-3,8-diones starting from readily available 1,4-naphthoquinones and alkynes under mild and clean conditions without using any photocatalysts is reported. The products could be obtained under blue LED (460 nm) irradiation at ambient temperature in 4 h with perfect regioselectivity and remarkable functional group tolerance. To discuss the special patterns of cyclobutene protons, to identify its cis-conformation, NMR spectra analysis (1D-NMR and 2D-NMR) was conducted in details by the chemical shifts, couplings and correlations. X-Ray Diffraction of 3ak confirmed its cis-conformation, and all the compounds were unequivocally confirmed by NMR, HRMS and XRD analysis. XRD analysis of 3ak further aids to disclose the reason why the cyclobutene and benzene rings are almost in the same plane.
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