Selective C–H Activation of Molecular Nanodiamonds via Photoredox Catalysis

While substituted adamantanes have widespread use in medicinal chemistry, materials science and ligand design, the use of diamantanes and higher diamondoids is limited to a much smaller number. Selective functionalization beyond adamantane is challenging as the number of very similar types of C–H bonds (2° and 3°) increases rapidly, and H-atom transfer does not provide a general solution for site selectivity. We report a new method using pyrylium photocatalysts that is effective for nanodiamond functionalization in up to 84% yield with exclusive 3° selectivity and moderate levels of regioselectivity between 3° sites. The proposed mechanism involving photooxidation, deprotonation, and radical C–C bond formation is corroborated through Stern–Volmer luminescence quenching, cyclic voltammetry and EPR studies. Our photoredox strategy offers a versatile approach for the streamlined synthesis of novel diamondoid building blocks.