Unlocking the Accessibility of Alkyl Radicals from Boronic Acids through Hydrogen-bond Assisted Organophotoredox Activation

Despite their prevalence in organic synthesis, the application of boronic acids (BAs) as alkyl radical precursors in visible-light assisted photocatalyzed reactions has been limited by their high oxidation potential. This study demonstrates the remarkable ability of amide solvents viz. DMA (N,N-dimethylacetamide) to participate in hydrogen-bonding interactions with BAs, thus enabling the modulation of their oxidation potential towards the generation of alkyl radicals. The developed protocol is simple, robust and demonstrates broad applicability for alkylation, allylation and elimination reactions in batch and continuous flow. The application towards dehydroalanine allows the synthesis of unnatural amino acids. Furthermore, the chemo-selective generation of radical species from BAs, in the presence of boronic ester-containing molecules, is now feasible, endorsing plausible boron-selective (bio-) orthogonal modifications.