Cobalt Mediated Reactions in Organic Synthesis

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This research is being funded by the Organic Synthesis Program. Dr. Krafft will be continuing her studies of the synthetic potential of cobalt carbonyl complexes as reagents for the controlled construction of five-membered rings. Reagents like this enrich the armamentarium of synthetic organic chemists and provide more powerful synthetic tools for the synthesis of more complex molecules. The work on the directed Pauson reaction has progressed to the point where one can now plan total syntheses with some confidence. The ene-yne cycloaddition is highly regioselective due to the direction by nitrogen or sulfur ligands tethered to the alkene. Further work is planned to improve the synthetic efficiency of the directed Pauson reaction. Some efforts are now directed toward the total synthesis of asteriscanolide. Two different approaches are being examined. An asymmetric modification of the Pauson cycloaddition is also under investigation. Other reactions using alkyne-cobalt carbonyls are underway, i.e. selective oxidations and sulfoxide reductions. The second part of the project involves the examination of reactions with acylcobalt carbonyl complexes. Earlier work demonstrated that butenolides, with a variety of substitution patterns, can be synthesized in high yield by the reaction of alkynes with acylcobalt carbonyl complexes. One major problem associated with the reaction will be addressed by the use of a directing ligand. The intermediate formed in the reaction is a pi-allyl cobalt complex. The carbon-carbon bond forming reactions of the pi-allyl complex will be investigated. Insertion of acyl cobalt complexes into alkenes and the asymmetric versions of these reactions will also be studied.