Remote C5-Selective Functionalization of Naphthalene Enabled by P–Ru–C Bond-Directed δ‑Activation

Site-selective
functionalization beyond the ortho-, meta-, and
para-positions on naphthalene derivatives is very challenging, especially
for the remote C5 position at the para-position of neighboring phenyl
rings. Herein, we report the remote C5-selective functionalization
of naphthalene via tertiary phosphine-induced ruthenium-catalyzed
δ-bond activation. This strategy over-rides traditional site
selectivity and efficiently installs different functional groups (alkyl,
fluoroalkyl, and aldehyde) in the C5 position with excellent regioselectivity
(C5/others >20:1). Moreover, this protocol is also suitable for
polycyclic
aromatic hydrocarbons and the more remote C8 position. Preliminary
mechanistic studies show that the tertiary phosphine group plays two
essential roles in the reaction: first, it assists the introduction
of Ru–C bond at the C8 position; second, due to the induction
effect, it assists the activation of the δ-bond by forming the
electron-donating P–Ru–C bond.