Asymmetric Tandem Michael Addition/Oxidation Of Pyrazolones With P-Benzoquinone Catalyzed By Cinchona Alkaloids

In recent years, cinchona alkaloids has elevated to the peerage in the kingdom of asymmetric catalysis. Undoubtedly, the position and value of cinchona alkaloids has been proved by the features of cheapness, easily to modify, efficiently and mildly to catalyze the conditions and friendly to the environment. Pyrazolones and quinones are commonly found in natural products, pesticides and medicines. Thus, the asymmetric synthesis of chiral pyrazolone derivatives, which have potential application value for the drug synthesis and discovery, from 4-substituted pyrazolones with p-benzoquinone by using natural cinchona alkaloids as catalyst was investigated.Herein, we report the first asymmetric tandem Michael addition/Oxidation of pyrazolones with p-benzoquinone catalyzed by cinchona alkaloids. The optimized reaction conditions were established after the study of the influence of various reaction parameters such as catalyst, solvent, oxidant, temperature, concentration and time. Under the optimal conditions, a variety of desired products were obtained in good yields (up to 82%) and excellent enantioselectivities (up to 99% ee). The products obtained were identified by 1H NMR, 13C NMR and HRMS. At the same time, we also studied the general process of this reaction and determined the byproducts affecting the yield.