Tandem Catalysis: Generating Multiple Contiguous Carbon−Carbon Bonds through a Ruthenium-Catalyzed Ring-Closing Metathesis/Kharasch Addition

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.