Arylation Of4-Substituted Pyrazolones With Diaryliodonium Salts

In recent years, hypervalent iodine compounds have received extensive attention in organic synthesis. Iodine(III) reagents with two carbon ligands, known as diaryliodonium salts, have been developed rapidly in recent decades. Because of their highly electron-deficient nature and excellent leaving-group ability, they are used as versatile arylating agents with many nucleophiles.With diaryliodonium salts as the arylating agent, the arylation of4-substituted pyrazolones promoted by organic bases was investigated. The results showed that tetramethylguanidine could promote the arylation efficiently, affording a series of pyrazolone derivatives. The effect of various reaction parameters such as base, solvent, temperature and concentration was investigated, and the optimal reaction conditions were established. The experimental results of the arylation of4-substituted pyrazolones indicated that all reactions were accomplished in two hours using achiral diaryliodonium salts as the arylating agent with good to excellent yields (up to97%), and when chiral diaryliodonium salts derived from methyl lactate were used as the arylating agent, all reactions were finished in96hours with ee value up to56%. All the arylation products were characterized by’H-NMR,13C-NMR and HRMS.Pyrazolone structural motifs are commonly found in natural products, pesticides and medicines. The synthesis of pyrazolone derivatives from4-substituted pyrazolones with diaryliodonium salts as the arylating agent was achieved, which has potential application value for the drug synthesis and discovery.