Isoindolin-1-one and isoquinolin-1-one are widely used as core backbones in natural products and important drug molecular structures. From the perspective of green chemistry and molecular diversity, it is particularly useful to develop general methods for constructing such structures. It is well known that synthetic metalloporphyrins are widely used as enzyme-like catalysts in the hydroxylation of benzyl C-H bonds. Similarly, N-hydroxyphthalimide (NHPI) can effectively mediate the activation of oxygen and be also widely used. Based on the previous work in the laboratory, this paper intends to combine 5,10,15,20-tetrakis(pentafluorophenyl) ferric chloride porphyrin (F20TPPFeCl) and NHPI to form a relay oxidation catalyst system, O2 is used as the terminal oxidant, the method that the bionic oxidation of cyclic benzylamine is realized at room temperature, it is very important to develop a green methodology for the construction of isoindolin-1-one and isoquinolin-1-one.
The main content of this paper includes the following three parts:
In the first part of this paper, it is reviewed that the synthesis progress of isoindolin-1-one and isoquinolin-1-one and the application of metalloporphyrins as imitation enzyme catalysts in oxidation reactions. Based on these designs, this subject of the paper was proposed and we would carry out these ideas.
In the second part of this paper, we explored the method about the oxidation of N-substituted-3,4-dihydroisoquinoline compounds using F20TPPFeCl/NHPI/O2 as the catalytic system. We found that the reaction is highly dependent on the N-substitution type. The alkyl group and the aryl group do not react, and only the acyl group which is pull electrons is the suitable substrates. Through optimization of the reaction conditions and selection of N-substituents, it was finally determined the acetyl and propionyl as the most suitable substituents, and N-substituted-3,4-dihydroisoquinoline: 0.5 mmol, F20TPPFeCl : 1 mol%, NHPI: 0.05 equiv., ethyl acetate (EA): 10 mL, room temperature, reaction for 8 hours, the yield of N-acetyl-3,4-dihydroisoquinolin-1-one reached 96%. Under the optimal conditions, we synthesized that the substrate extension of 1,2,3,4-tetrahydroisoquinoline and the corresponding N-substituted-3,4-dihydroisoquinolin-1-one derivatives, we had gotten the yield nearly 51% ~ 96%. The research on the hydrolysis of N-acetyl-3,4-dihydroisoquinolin-1-one derivatives was carried out, which enriched the pathway of post-functionalization.
In the third part of this paper, we continue to explore the method about the catalytic oxidation of N-substituted-isoindolin by F20TPPFeCl/NHPI/O2 system. The scope of the substrate for the catalytic oxidation system was further expanded. Firstly, we synthesized a series of N-substituted-isoindolin substrates through the acylation of isoindolin, the halogenation of o-xylene derivatives, and the amine cyclization reaction, and carried out oxidation studies on the optimal conditions. A series of isoindolin-1-one derivatives were synthesized with a yield of 27% ~ 82%.
Based on the above reaction results, we proposed that a possible relay oxidation mechanism of cyclic benzylamine.
The experimental results show that the catalytic system has good applicability to N-substituted benzylamine substrates, the catalyst and the catalytic system are environmentally friendly, the amount is small, and it has broad application prospects.