"The formation of new carbon-carbon bonds is of central importance in organic chemistry and a prerequisite for all life on earth. In this context, palladium catalysed cross-couplings have emerged as exceptionally powerful and useful methods for C-C bond formation. However, the reaction is largely limited to C(sp2)–C(sp2) bond formation. There are very few examples of cross couplings to form C(sp2)–C(sp3) or C(sp3)–C(sp3) bonds due to inherent problems associated with transition metals. As such a fundamentally new approach is required to solve this problem.
We plan to add aryllithium reagents to enantioenriched, secondary boronic esters and form intermediate boron-ate complexes. Subsequent one-electron oxidation of the aromatic ring would result in dearomatization leading to a radical cation which would trigger a 1,2-migration/rearomatization sequence. Exciting preliminary results involving sp2-sp2 bond formation shows that this novel concept is viable (using DDQ as oxidant) and we will study its development and in particular its application in the crucial C(sp2)–C(sp3) bond formation. We will explore organic and inorganic multi-electron oxidants as well as the use of emerging redox photocatalysis. The latter method has the potential to provide an especially green solution to the problem.
Even more exciting is the prospect of retaining the boron moiety after oxidation and 1,2-migration as this will allow the rapid construction of highly complex molecules. Once again preliminary results show that the concept is viable and will represent another significant step in organic chemistry. This methodology will be applied to the synthesis of challenging molecules."
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