Radical-initiated Unsaturated Hydrocarbon Functionalization Reactions

Radicals as unpaired electrons atoms or groups are generated by by the split of the covalent bonds atoms or groups under photochemical and themochemical conditions.Thus,the radical reaction is also called“free radical reaction”.Owing to its unique structural characteristics and high reactivity nature,radical chemistry has become one of the frontier areas of organic chemistry,and considerable achievements have been made to data.However,radicals are usually highly active,thus make the reaction disordered and the reaction sites uncontrollable.Discovering radical reactions that are easy to operate and control effectively still face many challenges.Both the oxidative radical strategy and visible-light photoredox strategy have becoming the important and straightforward methods in radical chemistry,which feature fast and high efficiency,good regioselectivity,and high atomic economy.Such strategies can both be used to construct two or more new chemical bonds in one step,which would play a crucial role in the synthesis of natural products,drug molecules and organic functional materials.With the continuous discovery of new methods and technologies that utilize the oxidative radical strategy and visible-light photoredox strategy in recent years,it has laid a basic foundation for industrial applications.This dissertation mainly dicussed radical-mediated functionalizations of unsaturated hydrocarbons the oxidative radical strategy and visible-light photoredox strategy.The contents of the dissertation are described in the following six chapters:In chapter 1,we review recent progress in radical-initiated functionalizations of unsaturated hydrocarbons.We focused on radical-mediated aryl migration reactions and radical-mediated 1,n-enyne cyclization reactions.including include aryl 1,2-migration,1,3-migration,1,4-migration,1,5-migration and 1,n-enyne cyclization with different types of radicals.In chapter 2,we summarize a visible light-induced 1,2-aryl migration reaction of allyl alcohols with?-carbonyl alkyl bromides for the synthesis of 1,5-dicarbonyl compounds.This method is successful by sequential alkylation of an alkene C–C double bond and intramolecular 1,2-aryl migration,and shows a broad substrate scope,excellent functional group tolerance and good selectivity.In chapter 3,a metal-free catalyzed oxidative radical aryl migration reaction of allyl alcohol and alkyl nitrile compounds is presented.In the presence of TBPB,a variety of?-aryl allylic alcohols underwent the 1,2-alkylarylation reaction with acetonitriles,giving products in good to excellent yields.This method proceeds via the C(sp~3)–H oxidative coupling with the C-C double bond and 1,2-aryl-migration,and represents a new access to acyclic molecules through metal-free oxidative alkene 1,2-alkylarylation.In chapter 4,a functionalization reaction of 1,n-alkyne and?-bromocarbonyl compounds via C(sp~3)-Br/C(sp~3)-H under the induction of visible light is introduced,which enable the one-step functionalization of both a C(sp~3)-Br bond and a C(sp~3)-H bond adjacent to the same carbon atom.This visible light photoredox catalysis offers a mild and straightforward access to diverse five-membered carbocyclic ring-fused polycyclic hydrocarbons with high turnover numbers(TONs;up to 4.93×10~3)and broad substrate scope.In chapter 5,the results of[2+2+2]oxidative radical cyclization reactions of N-(2-ethynylaryl)acrylamides with tertiary and secondary alkyl aldehydes has been developed.This reaction allows the formation of three new C-C bonds in a single reaction by a sequence of oxidative decarbonylation,radical addition across C-C unsaturated bonds,C-H functionalization and annulation,and represents the first oxidative decarbonylative[2+2+2]carbocyclization approach using tertiary and secondary alkyl aldehydes as a two carbon unit for assembling six-membered carbocycle-fused polycycles.In chapter 6,manganese-catalyzed intermolecular oxidative annulation of alkynes with?-vinyl aldehydes involving acylation and alkylation is described,thus providing a scenario for the divergent synthesis of bridged carbocyclic systems.By means of this manganese-catalyzed alkyne dicarbofunctionalization strategy,three chemical bonds,including two C-C bonds and one C-H bond,are formed via an aldehyde C(sp~2)-H oxidative functionalization/[4+2]annulation/protonation cascade.