Sulfur-mediated metal-free CH-CH cross-couplings

The development of new strategies for C-C bond formation is a critical activity with the potential to impact across the breadth of science. Of the synthetic tools developed in recent years for C-C bond formation, cross-coupling reactions involving aromatic and heteroaromatic building blocks hold high rank. More recently, metal-catalysed C-H functionalization has become an established and more atom-economical way to construct C-C bonds with a wide selection of directing groups available to control processes involving C-H bonds on aromatic rings. However, this strategy still requires one prefunctionalized coupling partner. So called cross-dehydrogenative coupling (CDC) strategies, or CH-CH-type cross-couplings, have therefore been developed that obviate the need for pre-functionalization of either coupling partner and allow the formation of new C -C bonds at the expense of a C-H bond in each of the two partners. Unfortunately, CH-CH couplings are mediated by platinium-group transition metals (e.g. iridium, ruthenium, rhodium, palladium and platinum) and this raises several issues: In addition to the cost and toxicity associated with their use, the supply of such metals is at risk and their use will become unsustainable. Furthermore, metal contamination in products arising from metal-catalyzed cross-coupling is a major concern in industry, particularly the pharmaceutical and organic electronic sectors. Finally, chemo- and regioselectivity, and a dependence on harsh reaction conditions and stoichiometric oxidants remain issues that limit the broad take-up of CH-CH-type coupling technologies. Thus, despite the remarkable recent advances in C -H cross-coupling, the development of metal-free CH-CH-type cross-coupling processes that use readily available non-prefunctionalized starting materials and that operate under mild conditions, remains an outstanding challenge of great importance in synthetic science. In this PhD project, we will develop sulfoxide-directed metal-free CH-CH cross-couplings of arenes with a range of alkyne and alkene partners to give products of C-H alkylation under mild conditions.