Department Chemie and Catalysis Research Center (CRC), Technische Universität München, Lichtenbergstrasse 4, 85747, Garching, Germany.
Angew Chem Int Ed Engl. 2017 Apr 3;56(15):4337-4341. doi: 10.1002/anie.201700837. Epub 2017 Mar 20.
1,3-Dithiane-protected enones (enone dithianes) were found to undergo an intramolecular [2+2] photocycloaddition under visible-light irradiation (λ=405 nm) in the presence of a Brønsted acid (7.5-10 mol %). Key to the success of the reaction is presumably the formation of colored thionium ions, which are intermediates of the catalytic cycle. Cyclobutanes were thus obtained in very good yields (78-90 %). It is also shown that the dithiane moiety can be reductively or oxidatively removed without affecting the photochemically constructed ring skeleton.
1,3-二硫杂环戊烯保护的烯酮（烯酮二硫杂环戊烯）在可见光照射（λ=405nm）下，在布朗斯台德酸（7.5-10mol%）存在下会发生分子内[2+2]环加成反应。反应成功的关键可能是有色硫翁离子的形成，这是催化循环的中间体。因此，环丁烷以非常好的收率（78-90%）得到。还表明，二硫杂环戊烯部分可以在不影响光化学构建的环骨架的情况下进行还原或氧化去除。
