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Media type:
E-Book
Title:
Electrochemical activation of strained donor-acceptor substituted carbocycles and selective hydrogenation of benzylic olefins by electroreduction
University thesis:
Dissertation, Universität Freiburg, 2023
Footnote:
Description:
Abstract: Donor–acceptor (D–A, D = aryl, A = malonate) cyclopropanes are readily available, masked 1,3-zwitterionic C3-synthons which are valuable building blocks for synthetic organic chemistry. Utilizing Lewis acid catalysis, the activated C–C single bond between the donor- and the acceptor-substituted carbon is easily cleaved allowing a variety of transformations from the formally generated zwitterionic form. Searching for new activation pathways an electrochemical approach that removes the need for Lewis acids was followed. Electrochemical activation of D–A cyclopropanes or cyclobutanes via anodic oxidation strategies paved the way for the synthesis of oxidized products by formal O2 insertion. Experimental and quantum-chemical mechanistic investigations were carried out on the reaction pathway, revealing the formation of a radical cation intermediate after C(sp3)-C(sp3) cleavage. Further research on this activation concept led to the development of a Friedel-Crafts-type arylation of D–A cyclopropanes and cyclobutanes.<br>Hydrogenation conveniently allows the construction of C(sp3)-centers from readily available olefins or alkynes while also providing orthogonality in protecting group strategies. However, the control of siteselectivity when more than one group that is affected by hydrogenation is present, is hard to achieve. This project started with a serendipitous discovery and was developed into a robust protocol that <br>overcame limitations of previously reported electroreductive methods for benzylic olefin hydrogenation. Known methods required aryl-EWG substitution on the alkene and used self-made electrochemical systems which hindered reproducibility. This procedure utilizes H2O or D2O for the selective hydrogenation and deuteration<br>of benzylic olefins when other C(sp2)/C(sp)-centers or protecting groups are present. In addition to a broad substrate scope (> 50 examples), experiments to support a mechanistic proposal were performed