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.