Co-Catalytic Coupling of Alkyl Halides and Alkenes: the Curious Role of Lutidine

Continuous pressure to shorten synthetic sequences along with the concomitant expansion of scope makes the use of alkyl bromides, chlorides, and oxygen based leaving groups- which are abundant and readily available feedstocks, highly attractive for C-C bond synthesis. However, selective activation of these bonds to generate radical intermediates remains challenging and is generally unfeasible using traditional activation strategies. Herein, we report a dual catalytic activation strategy to access primary, secondary, and tertiary alkyl radicals from respective alkyl chlorides and bromides, as well as primary tosylates and trifluoroacetates. While the method relies on visible light and a photocatalyst to facilitate electron transfer, based on reduction potentials, the substrates are not expected to be reduceable, and yet they are reduced in the presence of lutidine. Ultimately, our investigation revealed that lutidine was a precatalyst and ultimately led to the use of lutidinium iodide salt which served as a critical cocatalyst that resulted in improved reaction profiles. Our studies revealed two critical roles that lutidinium iodide salts play which made it possible to engage otherwise unreactive substrates: nucleophilic exchange and halogen atom transfer by the lutidinium radical. In short, this work converts unactivated alkyl chlorides, bromides, tosylates, and trifluoroacetates to radicals that can be used for C-C bond formation without the need for preactivation─effectively expediting synthesis.