Revealing the mechanisms of titanium-catalyzed umpolung reactions by a combined experimental and theoretical approach

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Titanium(III)-catalyzed reductive umpolung-reactions provide an elegant access to carbon-carbon bonds that cannot be formed in a direct fashion by other methods. Based on our previous works on ketone-nitrile and enone-ennitrile couplings, we will investigate the mechanisms of such reactions by a combination of experimental works and DFT-calculations. The main goal is to perform and understand the individual parts of the catalytic cycles and to develop models for the key-steps, especially the C-C bond forming events. The role of cationic intermediates and the participation of a second titanium(III)-species will be investigated in detail. In addition, it is our aim to provide an explanation for the high selectivities that we observed in our previously published enantioselective ketonitrile cyclization reaction. First results are provided that support the feasibility of each individual part of the research program. The conclusions from this project will have a major impact on the development of new reactions and catalyst generations in this field. They will provide a general understanding of reductive umpolung reactions and greatly facilitate future investigations in this research area.