Theoretical Studies On The Mechanisms Of Gold Catalyzed Cyclization Reactions Of 1,6-Diynes

The gold-catalyzed cyclization reactions of diynes are efficient routes for the constructions of cyclic skeletons.This thesis mainly studies the mechanisms of gold-catalyzed selective cyclizations of 1,6-diynes in different solvents.The potential energy surfaces for various possible paths were calculated by density functional theory?DFT?calculations.The key factors determining the selectivities of the reactions were discussed in combination with molecular structure analysis.The experimental phenomena were explained in depth.These results provided theoretical basis for mechanistic understanding and experimental design of the relevant reactions.This thesis mainly includes the following two aspects:?1?Theoretical study on the mechanism of gold-catalyzed 1,6-diynes cyclization in dichloromethane solution.The regioselectivity of the[3+2]-cyclization reaction of1,6-diynes,the whole reaction pathway,and the effect of SbF₆^-negative ions on the reaction pathway were studied by DFT calculations.Under the activation of triple bond by gold,the activity of the other alkynyl group is higher than that of the phenyl group in the nucleophilic cyclization step,forming a cyclic alkenyl gold intermediate.Further cyclization of the alkenyl cation with the phenyl group can realize the intramolecular[3+2]-cycloaddition reaction.Finally,the[3+2]-cyclization product is formed by continuous 1,2-hydrogen migrations.The results showed that the electronic effect of the alkyne and the steric hindrance effects are the key factors controlling the regioselectivity of the gold-catalyzed cyclization reaction.?2?Theoretical study on the mechanism of gold-catalyzed 1,6-diynes cyclization in methanol solution.The cyclization of 1,6-diynes in the methanol solution assisted by dual gold was studied by DFT calculations.Under this condition,a methoxy gold complex is formed firstly,which can undergo trans-nucleophilic addition to the gold-activated triple bond to obtain a 1,6-enyne intermediate having an alkenyl ether structure.An acetal is further formed from the enyne intermediate by gold-catalyzed5-exo-dig cyclization and nucleophilic attack of the solvent molecule.Finally,a five-membered ring product containing a carbonyl group could be formed by hydrolysis.The results show that steric hindrance is the main factor affecting the selectivities of both the methanol nucleophilic addition and the enyne cyclization steps.