Brønsted Acid Catalysis in Visible-Light-Induced [2+2] Photocycloaddition Reactions of Enone Dithianes.
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.
Department Chemie and Catalysis Research Center (CRC), Technische Universität München, Lichtenbergstrasse 4, 85747, Garching, Germany.
Christoph
C
Brenninger
Department Chemie and Catalysis Research Center (CRC), Technische Universität München, Lichtenbergstrasse 4, 85747, Garching, Germany.
Alexander
0000-0003-4663-3949
A
Pöthig
Department Chemie and Catalysis Research Center (CRC), Technische Universität München, Lichtenbergstrasse 4, 85747, Garching, Germany.
Thorsten
0000-0002-1342-0202
T
Bach
Brønsted acids; cycloaddition; diastereoselectivity; enones; homogenous catalysis; photochemistry