A Phosphine-Free Air-Stable Mn(II)-Catalyst for Sustainable Synthesis of Quinazolin-4(3<i>H</i>)-ones, Quinolines, and Quinoxalines in Water
Sucheta Mondal, Subhajit Chakraborty, Subhankar Khanra, Santana Chakraborty, Shrestha Pal, Paula Brandão, Nanda D. Paul
Abstract
The synthesis, characterization, and catalytic application of a new phosphine-free, well-defined, water-soluble, and air-stable Mn(II)-catalyst [Mn(L)(H 2 O) 2 Cl](Cl) ([ 1 ]Cl) featuring a 1,10-phenanthroline based tridentate pincer ligand, 2-(1 H -pyrazol-1-yl)-1,10-phenanthroline ( L ), in dehydrogenative functionalization of alcohols to various N -heterocycles such as quinazolin-4(3 H )-ones, quinolines, and quinoxalines are reported here. A wide array of multisubstituted quinazolin-4(3 H )-ones were prepared in water under air following two pathways via the dehydrogenative coupling of alcohols with 2-aminobenzamides and 2-aminobenzonitriles, respectively. 2-Aminobenzyl alcohol and ketones bearing active methylene group were used as coupling partners for synthesizing quinoline derivatives, and various quinoxaline derivatives were prepared by coupling vicinal diols and 1,2-diamines. In all cases, the reaction proceeded smoothly using our Mn(II)-catalyst [ 1 ]Cl in water under air, affording the desired N -heterocycles in satisfactory yields starting from cheap and readily accessible precursors. Gram-scale synthesis of the compounds indicates the industrial relevance of our synthetic strategy. Control experiments were performed to understand and unveil the plausible reaction mechanism.