DBU-Promoted Carboxylative Cyclization Of O-Hydroxy- And O-Acetamidoacetophenone With Carbon Dioxide

Carbon dioxide is one of the main greenhouse gases. In recent years, its concentration in the air keeps increasing. As a consequence, the utilization of carbon dioxide as C1 resource for synthesizing value-added chemicals has gained considerable attention. There are many advantages for carbon dioxide transformation into useful chemicals, since CO2 is inexpensive, readily available, non-toxic, non-flammable and renewable C1 source. However, the use of high-energy reactants and transition-metal catalysts usually is precondition for CO2-incorporaing reactions due to the thermodynamic and kinetic stability of carbon dioxide. These catalysts are generally expensive, not easy to store and might cause metal residues. Therefor, the exploration of the transition-metal-free reaction of carbon dioxide is highly desired.This thesis focuses on the transition-metal-free carboxylation reaction of carbon dioxide and the activation of a-C-H in some ketones. We found that a suitable base could remove one proton of a-C in ketones which is stable in polar solvent as enol tautomerism. After the reaction with carbon dioxide, carboxylation products were obtained. With the above knowledge in hand, here we built up a new carboxylation/intramolecular cyclization tandem reaction of o-hydroxy- and o-acetamidoacetophenone with carbon dioxide promoted by organic base 1,8-diazabicycloundec-7-ene (DBU).The reaction did not involve any transition-metal, and was performed at mild conditions. The optimize reaction conditions were established as followed:(1) o-hydroxy acetophenone with CO2:DBU(2 equiv), DMSO as solvent,80℃,24 h, derivatization reagent:n-C4H9I,80 ℃,4 h; (2) o-acetamido acetophenone with CO2:DBU(4 equiv), DMSO as solvent,80℃,24 h, derivatization reagent:CH3I,30℃,4 h. Using the above two reactions, a series of 4-hydroxy-2H-chomen-2-ones and 4-hydroxy-2(1H)-quinolinones were obtained in moderate to good yields. The substrate scopes of these two reactions were broad. An interesting acyl migration from nitrogen atom to carbon atom was observed in the reaction of o-acetamidoacetophenone.