Study On Claisen Rearrangement Of Allyl Aryl Ethers Using Environmentally Friendly Catalysts

The Claisen rearrangement of allyl phenyl ethers is a valuable reaction in organic synthesis having a variety of applications in perfumes, fragrances, foods, pharmacenticals and intermediate industries. Thus, Claisen rearrangement has received significant attention in―green‖chemistry.Since Claisen rearrangement discovery in 1912, its environmentally friendly catalysts are being continuously studied to improve the yield of the rearrangement products and regioselectivities, to shorten the reaction time and to perform the rearrangement under relatively milder conditions to prevent the undesired competitive side reactions and decomposition of the starting materials and/or products. The conventional catalysts for Claisen rearrangement were Lewis acids, Bronsted acids, and solid catalysts. However, a large amount of catalysts have complicated operation procedure, long reaction time, elevated temperature, low yield, low regioselectivity and using volatile solvents. The application of these catalysts is restricted due to their toxicity, corrosion, environment pollution and difficult recovery after reactions.Solid catalysts have advantages of high activity, convenience in handling, low toxicity, no corrosion, easy separation after completion of the reaction and reusability, which make them useful in green catalysis.In this thesis, Claisen rearrangement using environmentally friendly solid catalysts, such as silica-supported benzenesulfonic acid, nano-samarium oxide and TiO₂/Ag was investigated.The research includes four chapters:In chapter 1, the history and mechanism of Claisen rearrangement were introduced. The kinds of catalysts for Claisen rearrangement in recent years such as Lewis acids, Bronsted acids, solid catalysts and metal compounds were reviewed.In chapter 2, The Claisen rearrangement using silica-supported benzene sulfonic acid, instead of the traditional liquid acids, as catalysts was investigated under microwave irradiation. This protocol has advantages of short reaction time, high yield, high regioselectivity, no corrosion, no environmental pollution, and simple work-up procedure.In chapter 3, Samarium oxide nanoparticles, as basic catalysts, has been proved to be an efficient and reusable catalyst for Claisen rearrangement of allyl aryl ethers under solvent-free conditions at 160℃temperature. This protocol has advantages of high yield, high regioselectivity, short reaction time, no corrosion, no environmental pollution, and simple work-up procedure.In chapter 4, The Claisen rearrangement using TiO₂/Ag, instead of the traditional liquid acids, as catalysts was investigated under microwave irradiation. This protocol has advantages of short reaction time, high yield, high regioselectivity, no corrosion, no environmental pollution, and simple work-up procedure.