Studies On Intramolecular Multi-Site Reaction And Development Of Heterogeneous Palladium Catalyst For Coupling Reaction

Organometallic chemistry is not only a division subject of chemistry, but also an interdependent subject with organic and inorganic chemistry, which has a close relationship with petrochemistry industry, pharmaceutical industry and material science. Its development has broken the boundary between traditional organic and inorganic chemistry, and became a rising subject and a front field of modern chemistry. Many metal-catalyzed chemical reactions have played a fundamental role in the chemical industry.Carbon-carbon bond-forming reactions are not only the most widely used and important chemical transformation in the organic synthetic chemistry, but also a hot topic which the chemists pay attention to. During the development of organic chemistry, aldol- and Grignard-type reactions, the Diels–Alder and related pericyclic processes, and the Wittig andrelated reactions are such processes that have advanced our ability to construct increasingly complex carbon frameworks and, thus, enabled the syntheses of a myriad of organic compounds. In the past 30 years, metal-catalyzed carbon-carbon bond-forming reaction has enhanced considerably the prowess of synthetic organic chemists to assemble complex molecular frameworks and has changed the way we think about synthesis. In multitudinous transition metal catalyst (Fe, Ni, Cu, Pd, Rh, Ru…), the palladium catalysts have displayed the remarkable catalytic activity.Benzofurans and benzodifurans are important classes of oxygen-containing hetercyclic compounds, which play a fundamental role in organic chemistry and life science because of their presence in natural products and their interesting chemical and physiological properties. Benzofurans have been the subject of extensive studies and numerous synthetic methods have been developed for them. Benzodifurans have also received increasing attention because of their biological and pharmacological properties. But the reports on the synthetic method of them are still quite limited. In the chapter 2, we synthesized a series of dihydroxy dialkynylbenzenes and diacetoxy dialkynylbenzenes form hydroquinone and resorcin. we have developed a convenient synthesis of disubstituted benzodifurans in moderate to good yields by using a Pd(OAc)2-catalyzed double cyclization of bis(alkynyl)dihydroxybenzene and a one pot NaOH-mediated hydrolysis and double cyclization of diacetoxy dialkynylbenzenes. we have also developed an easy and efficient route for the synthesis of multi-substituted benzodifurans by using palladium-catalyzed double annulations of bis(allyloxy)bis(alkynylethynyl)- benzenes or bisalkynyldihydroxybenzene in the presence of allylic halides in good yield. It was also demonstrated that the products containing two 1,7-dienes moieties may be further utilized to build two aromatic rings to afford polycyclic conjugated aromatic compound via double RCM and oxidation reaction.During the past decade, olefin metathesis has become a very important and effective method for the construction of many functionalized carbocycles and heterocycles with the development of the highly active ruthenium and molybdenum carbene complexes. Enyne metathesis is also very interesting and useful in synthetic organic chemistry because the carbon-carbon double and triple bonds are cleaved forming a conjugated 1,3-diene, which was a useful synthon for various cycloadditions.Chromenes have received increasing attention due to their biological properties such as phototoxicity, anti-microbial activity, anti-juvenile hormone, anti-tumor, insecticidal and anti-feedant activities. Benzodipyrans-based compounds were designed as molecular probes for determining the steric restrictions of the agonist binding site of serotonin 5-HT2A and 5-HT2C receptors and have been found in plants. In the chapter 3, we developed an efficient synthesis of benzodipyrans and their analogues via intramolecular double enyne ring-closing metathesis. The difficultly synthesized benzo eight-membered ring products were formed in moderate to good yields when 10 mol % of Grubbs catalyst was added in two portions.Homogeneous catalyst generally showed better activity and selectivity than heterogeneous catalyst. However, homogeneous catalyst has two remarkable drawbacks. First, the expensive transition metal catalysts are difficulty to recover and reuse. Second, they often remain in the organic products at the end of the reactions, which is an extremely serious problem in the pharmaceutical industry because the level of heavy metals in active pharmaceutical intermediates is closely regulated. An efficient solution to the issue is the substitution of heterogeneous catalysts for their homogeneous counterparts.In chapter 4, we synthesized the mesoporous titanium phosphate (meso-TiP) material and prepared a heterogeneous palladoium catalyst (Pd@meso-TiP) by mixed meso-TiP and Pd(PhCN)2Cl2 in acetone at room temperature, then, explored its application in coupling reaction. First, we used the Suzuki coupling reaction of 4-iodoanisole and phenylboronic acid to optimize the reaction condition. In the research on the reusability of Pd@meso-TiP, we found that this catalyst could be recycled and reused six times without any obvious loss of its catalytic activity, which show remarkable stability and catalytic activity. Simple filtering can retrieve the catalyst from the reaction mixture after extraction with ethyl ether. Then, The scope of Suzuki coupling reaction between iodoarenes and arylboronic acid were studied. It was demonstrated that the catalytic systems have great tolerance. Iodioarenes with either electronwithdrawing substituents, such as NO2, COCH3, or CO2Bn, or electron-donating substituents, such as OMe, Me, or NH2 coupled readily with arylboronic acids in excellent yields. The substituent groups on arene ring in arylboronic acid had not obvious effect. The reactions of arylbromide containing electron-withdrawing substituents with arylboronic acid gave much better yields than the arylbromide containing electron-donating substituents. The coupling reactions of 1-bromonaphthalene or 4-bromobiphenyl with arylboronic acid formed the target products in moderat to excellent yields. The amount of Pd@meso-TiP in the coupling reaction between 4-bromoacetophenone and phenylboronic acid was also studied. It was demonstrated that the reaction could be completed in 97% yield within 8 hours. The catalyst could be reduced to 0.001 mol% and the turnover number (TON) based on Pd reached 99000 within 24 h. Furthermore, this heterogeneous catalyst, Pd@meso-TiP, was efficient for the Sonogashira and Heck reactions.