Direct Benzylic C-H Functionalization with Fluorenones under Visible-Light Irradiation.

An external photocatalyst-free benzylic C-H functionalization with fluorenones under visible-light irradiation has been achieved. This transformation provides an efficient synthetic approach to 9-benzylated fluorenols in ≤91% yield with 100% atom economy under mild conditions. Spectroscopic studies suggest that a reductive quenching of photoexcited fluorenones with toluene derivatives generates ketyl radicals and benzyl radicals, which undergo a cross-coupling to afford the desired fluorenols.