Theoretical Studies On Mechanisms Of Several Cyclization Reactions

Ring structure is a very common structure in organic compounds and is an important part of natural products.Cyclization is an important way to construct ring structure.The most common cyclization reaction is cycloaddition reaction.In this paper,the reaction mechanism and selectivity of four cyclization systems were studied using density functional theory(DFT).The results show that:(1)The cyclization step of the intramolecular aldehydes and carbon carbon double bonds with thioylide reagent to form a six membered ring structure needs the participation of more active ylide reagent DMSOM compared to2-(Dimethyl-?4-sulfanylidene)-1-phenylethanone.In addition,we explored the energy barriers of other side reaction paths of epoxy and cyclopropane formation,and found that from the theoretical calculation point of view,even if using DMSOM,epoxy and cyclopropane structures can still be generated,which is different from the conclusion of experimental research;(2)We explored the selective generation of 1,5-substituted1,2,3-triazole by azide and alkyne under the catalysis of Ag₂O.It is found that the cycloaddition reaction mechanism can be either the concerted reaction mechanism or the step-by-step reaction mechanism.And the reaction has good regioselectivity.(3)When we used the Pd(OAC)₂,Cu(OAC)₂,and Rh(OAC)₂catalysts for the cycloaddition of diazo compounds and isonitrile compounds to produce 1,4-substituted 1,2,3-triazole,the results show that these catalysts have good catalytic activity and regioselectivity,and have potential application value.(4)The homogeneous catalytic mechanism of an intramolecular allenynes reaction system was studied.The regioselectivity of the reaction which genereting[6+5]ring structure using Pauson-Khand and Alder-Ene reaction was studied by theoretical calculation.It was found that the molecule was more likely to react by P-K mechanism.The formation of the key intermediate to producing the product molecule(the coordination of carbon monoxide and rhodium)was thermodynamically spontaneous.At the same time,the double bond of the alldienyl in the reactant molecule away from the six membered ring is easy to participate in cycloaddition reaction to form[6+5]structure,and the intercarboxylation carbonyl is easy to add to the place near the benzene ring substituent.