Transition Metal-catalyzed Selective Conversion Of Unsaturated Bonds

With the vigorous development of organometallic chemistry,transition metal-catalyzed conversions of unsaturated bonds exhibit unique reactivity,and the efficient regulation of selectivity has become the research priority in this field.In this thesis,a highly selective transfer hydrogenation of carbon-carbon triple bonds was developed,which was extended to the reduction of nitrogen-containing unsaturated bonds.Furthermore,an enantioselective difunctionalization of carbon-carbon double bond was achieved.Firstly,a base-assisted metal species modulation mechanism enables Ni-catalyzed stereodivergent semihydrogenation of alkynes with water,delivering both olefinic isomers smoothly using cheap and nontoxic catalysts and additives.Different from most precedents,in which E-alkenes derive from the isomerization of Z-alkene products,the isomers were formed in orthogonal catalytic pathways.Mechanistic studies suggest base as a key early element in modulation of the reaction pathways:by adding different bases,nickel species with disparate valence states could be accessed to initiate two catalytic cycles toward different stereoisomers.The practicability of the method was showcased with nearly 70examples,including internal and terminal triple bonds,enynes and diynes,affording semi-hydrogenated products in high yields and selectivity.Further studies indicated that Ni-B-H₂O transfer hydrogenation system can be extended to the reduction of nitro group,affording the amino products.In addition,the transfer hydrogenation system with methanol as the hydrogen source also performed well in this reduction reaction.Azoarene was reduced to 1,2-diarylhydrazine in the Ni-catalyzed transfer hydrogenation system with methanol as hydrogen source,and the production of amino by-products can be suppressed by adjusting the amount of boron reagent.Based on our previous work of asymmetric catalysis,the last part of the dissertation investigated the highly enantioselective difunctionalization of alkenes.A palladium catalyzed enantioselective Heck/borylation reaction of alkene-tethered aryl iodides was realized,furnishing a variety of 2,3-dihydrobenzofuranyl boronic esters in high yield with excellent enantioselectivity.Asymmetric synthesis of chromane boronic ester,indane boronic ester and indoline boronic esters was also accomplished.