Studies On The Degradation Of Porphyrins And Related Reactions

The dissertation focuses on the degradation of porphyrins and related reactions. The paper comprises six chapters.Chapter 1. Introduction. This chapter presents brief overviews of the history of porphyrin chemistry and the breakdown of natural porphyrin products, and a more detailed and comprehensive overview about the chemical degradation of porphyrins.Chapter 2. Synthesis of 2,3-dibromo- and 2,3,12,13-tetrabromo-5,10,15,20-tetraarylporphyrins. Starting from tetraphenylporphyrin, undergoing metalation, nitration, demetalation, bromination, reduction, and denitration, Smith group developed a regioselective synthetic method for 2,3-dibromo-5,10,15,20-tetraphenylporphyrin. This approach was tractable in its operation and efficient in every step. However, it seemed somewhat troublesome and time-consuming. Here, we present an efficient one-pot synthetic method for the synthesis of 2,3-dibromo-5,10,15,20-tetraarylporphyrins by using 5,10,15,20-tetraarylchlorins as the starting materials. Namely, after refluxing 5,10,15,20-tetraarylchlorins with 2.2 equivalent NBS in ethanol-free chloroform under nitrogen for 4 h,4.0 equivalent DDQ was added, and refluxing was continued for 1 h, then, an excess of triethylamine was added,2,3-dibromo-5,10,15,20-tetraarylporphyrins were obtained in 95-96% yield after work-up. Starting from the same material, our method only needs 3 steps, and the last two steps can be conducted in one flask. Moreover, the overall yield of our method (70%) is higher than that of literature (57%). An improvement in the synthesis of 2,3,12,13-tetrabromo-5,10,15,20-tetraarylporphyrins had also been achieved during this courses. The increase rates were between 28% and 340%, depending on the electronic properties of the substituents at the meso-phenyl groups.Chapter 3. CuBr catalyzed degradation of Ni(Ⅱ) 2,3,12,13-tetrabromo-5,10,15,20-tetraarylporphyrins by the anion of E-benzaldoxime. We observed a serendipitous degradation of tetrabromoporphyrin in the reaction of Ni(Ⅱ) 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with the sodium salt of benzaldoxime, which led to the formation of chlorophin, secochlorin and porpholactone. When CuBr was used as a catalyst and the reaction temperature was 100℃, only chlorophin was obtainded in 30% yield. After optimization of the Cu(Ⅰ)-catalysed reaction conditions, chlorophin or bacteriophin could be obtained respectively with quite acceptable yields. Under similar conditions, other easily available tetrabromoporphyrins bearing different substituents at the at the meso-phenyl groups could also be subjected to smooth degradation to provide the corresponding chlorophins and bacteriophins.Then, some transformations of these brominated chlorophins, such as trifluoromethylation, Suzuki-coupling reactions, had been investigated. Finally, systematic studies on X-ray crystallographic structures and photophysical properties of a series of new chlorophins and bactriophins are also reported. The intense near-infrared absorptions of the porphyrins degradation products, especially bacteriophins, show promise as photosensitizers in PDT and as building blocks in electro-optical materials.Chapter 4. Degradation of 2,3,12,13-tetrabromo-5,10,15,20-tetraarylporphyrins by the anion of E-benzaldoxime in the absence of any catalyst. In the absence of CuBr, the products derived from the reaction of Ni(II) 2,3,12,13-tetrabromo-5,10,15,20-tetraarylporphyrins with the sodium salt of benzaldoxime are chlorophins, porpholactone, and secochlorin acid. After optimization of the reaction conditions, each of these compounds can be obtained respectively with quite acceptable yields. On the basis of experimental results together with the related reports, a possible mechanism for the formation of chlorophins, porpholactone and secochlorin acid is proposed. Finally, studies on the chemical transformations, X-ray crystallographic structures and photophysical properties of porpholactones are also reported.Chapter 5. Dess-Martin Periodinane mediated oxidative ring-opening reactions of tetraphenylporphyrin. Tetraphenylporphyrins were found to be oxidized in the presence of Dess-Martin Periodinane to afford open-chain tetrapyrrolic compounds. The central metal ions of the substrate porphyrins played an important role in those reactions.Chapter 6. Synthesis of porphyrins bearing two fused rings.2,3-Dibromo-5,10,15, 20-tetrakis(1-naphthyl)porphyrin and its zinc complex were prepared by using the method we developed in Chapter 2, which can be converted into porphyrins bearing two fused six-membered rings by palladium-catalyzed intramolecular cyclization reaction.