Silica Sulfuric Acid Catalyzed Synthesis Enamine Under Mild Conditions And Mediated Acylation Of Amines With 1,3-diketones Via C-C Bond Cleavage

An inexpensive and lower corrosive silica sulfuric acid was utilized as catalyst for the synthesizing enamine under mild conditions (room temperature),and acylating amines with 1,3-diketones via C-C bond cleavage with higher temperature. In this chemistry, no solvent and transient metal catalyst was used, and the oxygen and/or water were important for the cleavage of C-C bond. The mechanistic insights showed that both acid catalyzed hydrolytic C-C bond cleavage and hydroxyl radical oxidative C-C bond cleavage were co-existed. The activation effect of SSA on molecular oxygen was observed. In the oxidative path, the hydroxyl radical was detected both in the reaction system and SSA at oxygen atmosphere by using 4-benzamido-2,2,6,6-tetramethylpiperidine (4-BATMP) as radical scavenger, and the side products acetone, formic acid, acetic acid were detected by gas chromatography(GC) and ion chromatography(IC) respectively. The evidence perfectly proved mechanism of the reaction.The first part focused on the application of SSA as catalyst for the synthesis of enamine under mild conditions. SSA solid acid catalyst was prepared by using inexpensive silica gel. Then SSA was utilized to catalyze the condensation of both aromatic amines and aliphatic amines with 1,3-diketones under solvent free conditions to obtain enamine derivative in moderate to good yields. This process displayed several advantages, such as good selectivity, high yields, easily handling and so on.The second part mainly focused on the application of SSA on catalytic C-C bond cleavage acylation of amines with 1,3-diketone as acylation agent.(oxygen atmosphere to aromatic amines, nitrogen atmosphere to aliphatic amine) to form amide. The optimized reaction condition was achieved by investigating different reaction temperature, solvents, the amounts of catalyst. The reaction was carried out in oxygen atmosphere(nitrogen atmosphere for aliphatic amines) at 120℃(140℃) by using SSA as catalyst. This procedure could be applied to a wide scope of amines and β-diketones, easily handling, high selectivity and mediate to good yield (39-99%), which provides a simple way of thinking of C-C bond cleavage without transition metal catalyst.