Efficient Synthesis of Benzimidazole and Quinoline Derivatives Catalyzed by Functionalized Amidato Ruthenium Complexes in Water via Acceptorless Dehydrogenative Coupling Strategy

Abstract

Transition-metal-catalyzed acceptorless dehydrogenative coupling (ADC) has emerged as a sustainable synthetic strategy for the construction of N-heteroaromatics. Herein, a series of watersoluble amidato Ru catalysts were designed, synthesized, and utilized in the selective synthesis of 2-substituted benzimidazoles from the aromatic diamines and primary alcohols, as well as 2-substituted quinolines from the substituted 2-aminobenzyl alcohols and acetophenones via the ADC strategy in water. Catalyst 1 d bearing a strong electron-donating hydroxyl group on the ligand exhibited the best catalytic activity. The catalytic system demonstrated remarkable efficiency and versatility, allowing for the application of over 40 substrates in two ADC reactions with good to high yields. Based on control experiments and density functional theory (DFT) calculations, a plausible mechanism was proposed, highlighting the significant role of functionalized amidato Ru complexes in catalyzing alcohol dehydrogenation via an outer-sphere pathway.

Cu-catalyzed convenient synthesis of 2-trifluoromethyl benzimidazoles via cyclization of o-phenylenediamines with hexafluoroacetylacetone

“…In the course of our continuous research on the development of novel methods for the preparation of fused aromatic heterocycles, 9 we achieved the efficient synthesis of 2-trifluoromethyl benzimidazoles through the cyclization reaction of various o -phenylenediamines with hexafluoroacetylacetone in the presence of Cu 2 O as the pre-catalyst under extra ligand-free conditions (Scheme 1b). The results are described in this paper.…”