Regioselective Heck Coupling Reactions : Focus on Green Chemistry
Abstract: Carbon-carbon bond formation reactions are among the most important processes in chemistry, as they represent key steps in the synthesis of more complex molecules from simple precursors. This thesis describes mainly the development of novel regioselective applications of the mild and versatile palladium-catalyzed carbon-carbon coupling method, commonly known as the Heck reaction. In addition, this thesis will focus on environmentally friendly developments of the Heck reaction.Novel ligand-controlled internal Heck vinylations of vinyl ethers and enamides to form branched electron-rich dienes were performed with high regioselectivity. The vinylation of 2-hydroxyethyl vinyl ether permits a chemoselective transformation of a vinylic triflate or bromide into a blocked α,β-unsaturated methyl ketone. Furthermore, a simple separation of the palladium catalyst was achieved with new fluorous-tagged bidentate ligands in combination with fluorous solid phase extraction. The reaction times could be reduced up to 1000 times with controlled microwave heating in the palladium-catalyzed reactions with, in the majority of cases, retained, high selectivity. The development of a “green” regioselective arylation and vinylation method relying on an aqueous DMF-potassium carbonate system and excluding the toxic thallium salt has been accomplished. Ionic liquids as the versatile and environmentally friendly class of solvents have been used in rapid phosphine-free terminal Heck arylations with controlled microwave heating. Recycling of the catalytic medium was achieved after a simple product purification.
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