Ruthenium catalyzed dehydrogenative α-C–H functionalization of β-naphthol using alcohols: a metal–ligand cooperative borrowing hydrogen approach

Abstract

Chemoselective α-C–H functionalization of β-naphthol is achieved with inexpensive and readily available alcohols using a well-defined, air-stable, and easy-to-prepare Ru(II)-catalyst (1a) bearing a redox-active tridentate pincer (L^1a). Only 1.0 mol% of 1a showed promising catalytic efficiency, producing various α-alkylated β-naphthols in moderate to good isolated yields starting from different aromatic, hetero-aromatic, and aliphatic alcohols, including methanol, ethanol, and other long-chain alcohols. 1a also efficiently catalyzes the α-C–H alkylation of β-naphthols using aromatic diols as the di-alkylating agent. 1a also exhibited promising results during the large-scale synthesis of α-alkylated β-naphthols. Mechanistic investigation revealed that the 1a-catalyzed α-C–H functionalization of β-naphthol proceeds via a borrowing hydrogen path where hydrogen is transferred from alcohol to the azo-chromophore of the tridentate pincer via a transient ruthenium hydride intermediate, which was transferred in the later stage to the in situ formed alkylidenenaphthalen-2(1H)-one intermediate, producing α-alkylated β-naphthols as the final product.