Polyoxometalate-Based Metal–Organic Frameworks with Both Proton Acid and Multioxidative Active Sites: Highly Efficient Catalytic Synthesis of Quinazolinones

Quinazolinone derivatives are an important class of pharmaceutical and pesticide intermediates, which are generally synthesized starting with the condensation reaction between aldehydes and 2-aminobenzamide to obtain corresponding intermediates and then oxidized to obtain the products. Although some catalysts have been developed currently for the synthesis of quinazolinone derivatives, their catalytic efficiency is relatively low because only the oxidative catalytic sites of the catalyst have been focused on. Herein, we synthesized three new polyoxometalate-based metal-organic frameworks, [Cu^I₄(4,4'-bipy)₇(H_<i>n</i>-1PMo_12-<i>n</i>V_<i>n</i>O₄₀)]·2H₂O (<i>n</i> = 1-3), which were formed by coordinating a Cu(I)-bipy complex with different Keggin-type phosphomolybdic acids. An important feature of these compounds is that they possess proton and multioxidative active sites [Cu(I) center and V(V) center]; thus, we applied them to the catalytic synthesis of quinazolinone derivatives. The results indicate that compound <b>3</b> has an excellent catalytic activity. Based on density functional theory calculations, it is speculated that protons participate in the aldehyde amine condensation reaction, which changes the reaction pathway and reduces the activation energy from 55.1 to 31.4 kcal/mol, thereby increasing the reaction rate significantly. Interestingly, Raman spectra and electron paramagnetic resonance measurements indicate the presence of Cu^IIOO^• and ^•O₂^- during the oxidative dehydrogenation process, which facilitates the rapid consumption of 2-phenyl-2,3-dihydroquinazolin-4(1<i>H</i>)-one intermediates, thereby promoting the chemical reaction to move toward the positive direction. Thanks to the synergistic effect of multicatalytic sites, compound <b>3</b> achieved highly efficient catalytic synthesis of quinazolinones with 99% yield in 1 h.