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Tandem catalysis: generating multiple contiguous carbon-carbon bonds through a ruthenium-catalyzed ring-closing
Benjamin A Seigal1, Cristina Fajardo, Marc L Snapper
1Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, USA.
Abstract:
Tandem catalysis can offer unique and powerful strategies for converting simple starting materials into more complex products in a single reaction vessel while generating less waste and minimizing handling. In this regard, Grubbs' ruthenium alkylidene (Cy3P)2Cl2Ru=CHPh is shown to catalyze two mechanistically distinct transformations to offer a unique protocol that effects multiple bond changes in a single operation. A tandem ruthenium-catalyzed olefin ring-closing metathesis (RCM)/Kharasch addition allows for the facile preparation of bicyclic [3.3.0], [4.3.0], and [5.3.0] ring systems in one step from the appropriately functionalized acyclic precursors. For substrates where the intramolecular Kharasch addition fails, an intermolecular Kharasch addition is possible. By combining the intra- and intermolecular Kharasch additions with RCM, three new contiguous carbon-carbon bonds with multiple stereocenters can be generated by the ruthenium catalyst in a controlled fashion in one operation through two mechanistically distinct pathways.
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