Visible Light-catalyzed Oxidative Dimerization Of Unsaturated Hydrocarbons

Visible light photocatalysis is an emerging field of chemistry in recent years.It uses visible light as the green and widely existed energy,and photocatalyst that has a strong absorption in the visible region as a medium to trigger organic reactions via single electron transfer or energy transfer pathway.Comparing with traditional thermal reactions and UV light-induced photoreactions,visible light-mediated reactions have the advantages of energy-saving,green and safe,leading to a wider substrate scope and easy handling.It meets the requirements of green and eco-sustainable chemistry,and has already been one of the hot topics.This work started from unsaturated hydrocarbons such as alkenes and alkynes,with dioxygen in the open air as the green oxidant,thoroughly studied the oxidative dimerization reactions of unsaturated hydrocarbons via different pathways using visible light photocatalysis as a tool.The thesis is divided into five chapters.In chapter one,the research background and reaction principles of visible light photocatalysis are reviewed.Research progress on visible light photocatalytic reactions proceeded via radical cation of alkenes and alkynes as well as energy transfer is summarized in details.The thesis proposal is presented,too.In chapter two,we developed a photoredox catalytic protocol for the synthesis of naphthalene derivatives from readily available styrenes using 9-mesityl-10-methylacridinium perchlorate as photocatalyst via a tandem mechanism of electrophilic addition/Friedel-Crafts cyclization/radical coupling/elimination sequence.In the reaction 2-phenylmalononitrile was used as the co-catalyst,which effectively promoted the formation of the naphthalene products.By controlling the reaction conditions,3,4-dihydronaphthalen-1(2H)-ones and(dihydro)naphthalenes were achieved in the open air and under nitrogen atmosphere,respectively.In chapter three,we introduced a mild visible light induced photocatalytic system for the highly stereoselective synthesis of 1,4-enediones.The reaction started directly from aryl alkyne precursor,using green dioxygen as terminal oxidant.Both E-and Z-isomer can be selectively synthesized by controlling the reaction conditions.Visible light plays multiple roles in cis-alkenes synthesis: sensitizing photocatalyst,supplying energy to increase the proportion of active intermediates and promoting the transformation of products to the Z-isomer.In chapter four,we studied the intramolecular and intermolecular [2+2] cycloaddition reaction via “triplet-triplet” energy transfer pathway using conjugated dienones as the substrate,and synthesized a series of cyclobutene and cyclobutane derivatives which have large ring tension.Mechanism was verified from several aspects to demonstrate the possibility of energy transfer pathway.Chapter five gives the out look of visible-light photocatalysis.