Visible Light-Induced Amine Oxidation Reactions

As a novel and green catalytic strategy, visible light-induced photoredox catalysis has been well applied to organic synthesis in the past several years. In this dissertation, recent advances in the research area were reviewed in detail and the related visible light-induced amine oxidation reactions were investigated. The detailed works are listed as below:First, we synthesized chiral diamines from commercially available natural amino acids and applied them to visible light-induced intramolecular cyclization reactions, affording the corresponding tetrahydroimidazoles in excellent yields and selectivities (up to 94% yield,> 19:1 dr). We found that the trans-product could be converted into the thermodynamically more stable cis form after prolonged the reaction time. And two pathways were proposed to explain the epimerization based on the results of control experiments.Meanwhile, we further applied the visible light-induced amine oxidative functionalization reaction to the construction of isoquino[2,1-α][3,1]oxazine and isoquino[2,1-α]pyrimidine frameworks. The method directly used air as the terminal oxidant. After carefully screening the reaction parameters we obtained the best reaction conditions and investigated the electronic and steric effect on the reaction efficiency. We also found that the reaction still occurred smoothly when the reaction scale was extended to gram scale or directly used organic dye as the photocatalyst.Moreover, a photocatalytic formal [3+2] cycloaddition of 2H-azirines with alkynes has been achieved under irradiation by visible light in the presence of organic dye photocatalysts. This transformation provides efficient access to highly functionalized pyrroles in good yields and has been applied to the synthesis of drug analogues HMG-CoA. A primary trial of photocascade catalysis merging energy transfer and redox neutral reactions was shown to be successful. Finally, a plausible reaction was proposed based on the results of many mechanism studies and literature reports.We have developed a novel and highly selective photocatalytic visible-light method for desulfonylation of tosyl amides using Hantzsch ester as the reductive quencher and hydrogen source. Comparing with the reported dprotection method, this N-S bond cleavage process featured mild reaction conditions with broad substrate scopes and well tolerated several functional groups. The preparative utility of this methodology was well illustrated by gram-scale and sun light irradiation reactions. Based on the literature report, a plausible reaction mechanism was also proposed.In addition, an efficient visible light-induced C-S bond activation reaction of,β-ketosulfones that operates under mild reaction conditions has been repored. It renders this reaction a useful method to various symmetrical and unsymmetrical 1,4-diketones from readily available starting materials. Furthermore, the desired products were well applied to the construction of synthetically significant pyrrole, furan, and thiophene frameworks. A plausible reaction mechanism was proposed based on the mechanism studies including radical trapping experiment, light on-off experiment, CV studies, DFT calaulation and GC-MS experiments.We have reported an unprecedented α-allylation of amines by combining palladium catalysis and visible-light photoredox catalysis. In this dual catalysis process, the catalytic generation of allyl radical from the corresponding π-allylpalladium intermediate was achieved without additional metal reducing reagents (redox-neutral). Various allylation products of amines were obtained in high yields through radical cross-coupling under mild reaction conditions (27 examples, up to 84% yield). Moreover, the transformation was applied to the formal synthesis of 8-oxoprotoberberine derivatives which show potential anticancer properties. The existence of the allyl radicals and a-amino radicals were well proved through radical trapping experiments and EPR studies.Finally, a novel and efficient C-P bond formation reaction of diaryl-phosphine oxides with aryl iodides was achieved by combining nickel catalysis and visible light-induced photoredox catalysis has been described. This dual-catalytic reaction showed broad substrate scope, excellent functional group tolerance and afforded the corresponding products in good to excellent yields. Compared with the previously reported use of photoredox/nickel dual catalysis in the construction of C-C bonds, the methodology described herein was observed to be the first to allow for the C-heteroatom bond formation.