Department Chemie and Catalysis Research Center (CRC), Technische Universität München, 85747 Garching, Germany.
Org Biomol Chem. 2019 Aug 14;17(30):7192-7203. doi: 10.1039/c9ob01146c. Epub 2019 Jul 23.
Despite the importance of cyclobutanes there are not many direct [2 + 2] photocycloaddition reactions which can be performed with visible light in the absence of a catalyst. A notable exception is the reaction of 1-aryl-2-nitroethenes and olefins which can be performed at a wavelength of λ = 419 nm or λ = 424 nm in CHCl as the solvent. In the present study, a total of 15 1-aryl-2-nitroethenes were found to undergo a [2 + 2] photocycloaddition with 2,3-dimethyl-2-butene (28-86% yield) and a set of 12 olefins was studied in their photocycloaddition to 1-phenyl-2-nitroethene (37-88% yield). All mechanistic results are in agreement with a triplet reaction pathway and with the intermediacy of a 1,4-diradical.
尽管环丁烷很重要，但在没有催化剂的情况下，能用可见光进行的直接[2+2]光环加成反应并不多。一个值得注意的例外是 1-芳基-2-硝基乙烯和烯烃的反应，它们可以在溶剂 CHCl 中于波长λ=419nm 或λ=424nm 下进行。在本研究中，共发现 15 种 1-芳基-2-硝基乙烯与 2,3-二甲基-2-丁烯（产率 28-86%）发生[2+2]光环加成反应，并研究了一组 12 种烯烃与 1-苯基-2-硝基乙烯（产率 37-88%）的光环加成反应。所有的机理结果都与三重态反应途径一致，并与 1,4-双自由基中间体一致。
