Polyoxometalate-Based\nMetal–Organic Frameworks\nwith Both Proton Acid and Multioxidative Active Sites: Highly Efficient\nCatalytic Synthesis of Quinazolinones

Quinazolinone derivatives are an important class of pharmaceutical\nand pesticide intermediates, which are generally synthesized starting\nwith the condensation reaction between aldehydes and 2-aminobenzamide\nto obtain corresponding intermediates and then oxidized to obtain\nthe products. Although some catalysts have been developed currently\nfor the synthesis of quinazolinone derivatives, their catalytic efficiency\nis relatively low because only the oxidative catalytic sites of the\ncatalyst have been focused on. Herein, we synthesized three new polyoxometalate-based\nmetal–organic frameworks, [Cu<sup>I</sup><sub>4</sub>(4,4′-bipy)<sub>7</sub>(H<sub><i>n</i>–1</sub>PMo<sub>12–<i>n</i></sub>V<sub><i>n</i></sub>O<sub>40</sub>)]·2H<sub>2</sub>O (<i>n</i> = 1–3), which were formed by\ncoordinating a Cu(I)-bipy complex with different Keggin-type phosphomolybdic\nacids. An important feature of these compounds is that they possess\nproton and multioxidative active sites [Cu(I) center and V(V) center];\nthus, we applied them to the catalytic synthesis of quinazolinone\nderivatives. The results indicate that compound <b>3</b> has\nan excellent catalytic activity. Based on density functional theory\ncalculations, it is speculated that protons participate in the aldehyde\namine condensation reaction, which changes the reaction pathway and\nreduces the activation energy from 55.1 to 31.4 kcal/mol, thereby\nincreasing the reaction rate significantly. Interestingly, Raman spectra\nand electron paramagnetic resonance measurements indicate the presence\nof Cu<sup>II</sup>OO<sup>•</sup> and <sup>•</sup>O<sub>2</sub><sup>–</sup> during the oxidative dehydrogenation process,\nwhich facilitates the rapid consumption of 2-phenyl-2,3-dihydroquinazolin-4(1<i>H</i>)-one intermediates, thereby promoting the chemical reaction\nto move toward the positive direction. Thanks to the synergistic effect\nof multicatalytic sites, compound <b>3</b> achieved highly efficient\ncatalytic synthesis of quinazolinones with 99% yield in 1 h.