Study Of Cobalt-Catalyzed Asymmetric Ring-Opening Reaction Of Heterobicycloalkenes And Hydrosilylation Of Enynes

Metal-facilitated asymmetric catalysis is an important approach to synthesize chiral compounds.Among them,precious metal catalysts such as rhodium,palladium,platinum,and iridium have advantages of high reactivity and low catalyst loading,but they are expensive,low abundant in nature,and relatively toxic.On the other hand,metal catalysts derived from first-row transition metals of low price have attracted great attentions and various activity achievements have been obtained.Cobalt metal is in the same group as rhodium and exhibits significant catalytic activity in organic catalysis.In current dissertation,highly active cobalt catalyst systems for the asymmetric ring-opening reaction of heterobicycloalkenes and hydrosilylation of enynes were developed.Although a variety of catalyst systems have been reported for transition-metal catalyzed asymmetric ring-opening reactions of heterobicycloalkenes,the study of cobalt catalysis is still insufficient.In this dissertation,the reaction between1,4-dihydro-1,4-epoxynaphthalene and（E）-styrylboronic acid were used as model to screen and optimize the ligands,cobalt salts,solvents and temperatures required in the cobalt catalyst system.The optimal catalytic system[（R,R）-Ph-BPE/CoI₂/K₂CO₃)]was further applied in the exploration of substrate scopes.36 types of substituted cyclohexenes with various functional groups were successfully prepared in high yield and high enantioselectivity under mild conditions and simple operation.Alkenyl silanes are important building blocks to construct versatile organosilicone.Metal-catalyzed hydrosilylations to synthesize alkenyl silanes are the most economical and direct method.Few studies about cobalt-catalyzed hydrosilyation of enynes were reported.In this dissertation,reactions between phenyl-substituted 1,3-conjugated enynes and phenylsilanes were selected as model reaction to screen the ligands,cobalt salts and solvents of the cobalt catalytic system.The optimal catalyst system is dpppent/Co（OAc）₂/1,4-dioxane.The substrate scope was explored using the optimal catalyst system and a series of dienyl silanes were synthesized in high yields.The advantages of current cobalt-catalyzed route are mild reaction conditions,high yield and excellent regioselectivity.