Overcoming the Limited Reactivity of 1‑Naphthaldimine in C–H Alkylation with Alkyl Halides by a Robust Ru Catalyst

Site-selective C–H alkylation with alkyl halides
was restricted
to strong and stable coordination groups that enhance the nucleophilicity
of transition metals for a favorable oxidative addition. Herein, we
report that a bench-stable ruthenium catalyst Ru(benzene)(OPiv)2 can overcome the insufficient reactivity of an unstable aldimine
group and enable a regioselective alkylation of naphthalene with alkyl
iodides. A wide range of primary and secondary-alkylated naphthalene
derivatives have been achieved without external oxidants or additives,
illustrating their good functional group compatibility and efficiency
in conversion yields. Detailed mechanistic studies and reactivity
investigations reveal that the smaller size of the evaporable benzene
ligand in the catalyst had superior reactivity to promote the C–H
activation and ligand-exchange reaction than p-cymene.
The chemo- and regioselectivity of C2–H alkylation on naphthaldimines
may result from the formation of an active spiro[5.5] Ru-species participating
in the direct oxidative addition of alkyl iodides. Our findings open
a new avenue for C–H alkylation promoted by a directing group
with insufficient reactivity and show possible application scenarios
in the preparation of polyaromatic natural products.