Transition Metal-catalyzed Diels-Alder Reactions Of2-alkylbenzaldehydes And Unsaturated Hydrocarbon

2-Alkylbenzaldehyde is a compound with many reaction sites, which was widely used tosynthesize cyclic compounds by synthetic chemists recently. We systematically studiedtransition metal-catalyzed Diels–Alder Reactions of2-Alkylbenzaldehydes and unsaturatedhydrocarbon. We have initially developed an efficient and practical method for the synthesisof naphthalene derivatives via silver-catalyzed benzannulation of enynal with bromoalkyne oralkyne. In exploring a variety of reactions of2-alkylbenzaldehyde, it was unexpectedly foundthat NHC-gold can catalyze a bioinsipred tandem Diels–Alder/Diels–Alder reaction of anenynal and a1,3-diene to rapidly construct the highly-strained benzotricyclo[3.2.1.02,7]octaneskeleton. However, a tandem Diels–Alder/Friedel–Crafts reaction occurred instead whensilver salts were used as the catalyst, which only obtained another structurally interestingbridged compound.The thesis can be summarized as the following two parts:Part One: Silver-catalyzed benzannulation of enynal with bromoalkyne or alkyne tonaphthalene derivativesOwing to the disadvantages of the reported method for the synthesis of naphthalenederivatives, such as expensive catalysts or additive, we developed an efficient and practicalmethod for the synthesis of naphthalene derivatives via silver-catalyzed benzannulation ofenynal with bromoalkyne or alkyne. This reaction proceeded smoothly without additive.Moreover, this system holds the advantages of excellent regioselectivity and wide substratescope. Except for simple alkynes, bromoalkynes, dialkynes and trialkynes are tolerated,yielding bromo-naphthalene derivatives and more complex naphthalene derivatives withmany benzene rings. Bromine atoms could be introduced into the naphthalene skeleton whenbromoalkynes were used as substrates. With the bromo-naphthalenes in hands, we thenexplored the further useful chemical transformations.Part two: Gold or Silver-catalyzed Diels–Alder reaction of enynals with1,3-dienes1) In exploring a variety of reactions of2-alkylbenzaldehyde, it was unexpectedly foundthat NHC-gold can catalyze a bioinsipred tandem Diels–Alder/Diels–Alder reaction of anenynal and a1,3-diene to rapidly construct the highly-strained benzotricyclo[3.2.1.02,7]octane skeleton. The reaction was proposed to proceed through the intramolecular Diels-Alderreaction of an in situ-generated vinyl-substituted cyclic-o-QDM. The detail controlexperiments indicated that a pyrylium intermediate with a1,3-diene proceeded the ionicstepwise Diels-Alder reaction mechanism when NHC-gold was used as the catalyst. Thissystem has the advantages of the mild reaction conditions, excellent substrate scope and highfunctional group tolerance.2) In exploring Gold-catalyzed Diels–Alder reaction, it was accidentally found that atandem Diels–Alder/Friedel–Crafts reaction occurred instead when silver salts were used asthe catalyst, which only obtained another structurally interesting bridged compound. Differentfrom Gold-catalyzed reaction mechanism, a pyrylium intermediate with a1,3-diene proceededa concerted Diels-Alder reaction mechanism when silver salts were used as the catalyst. Thecontrol reactions revealed that only cis-isomers of1,3-butadienes could be converted into thebridged products. Furthermore, silver can catalyze a tandem Diels–Alder/-H elimination ofan enynal and a1,3-diene to form the dihydronaphthalene skeleton.