Theoretical Studies On Mechanism Of W?co?₅-catalyzed Cycloisomerization And Rh₂?esp?₂-catalyzed 1,2-migration Reaction

Quantum chemical calculation has been an important branch in the development of modem chemistry.With the help of some calculation softwares(e.g.,Gaussian),some experimental phenomena can get a reasonable interpretation under molecular level.Combined with the progress of experimental means,modem chemistry will continue to rapid development.The W-catalyzed cycloisomerization of the bicyclo[4.1.0]substrate and the Rh-catalyzed 1,2-migrations of the diazoacetates were investigated using density functional theory(DFT),not only clarified the mechanism of reactions,but also revealed the role of catalyst in the reactions and reasonably explained some experimental phenomena.Therefore,this research can provide theoretical guidance for the derivation of reaction mechanism is helpful for understanding and controlling more chemical reactions and that is of great academic significance.The main research contents and conclusions are as follows.Firstly,the cycloisomerization of the bicyclo[4.1.0]substrate into 4,5-dihydro-benzo[b]furan was investigated using density functional theory(DFT).Comparative studies on four models(Model ?:with W(CO)5 and NEt3;Model ?:without NEt3;Model ?:without W(CO)5;Model ?:without W(CO)5 and NEt3)indicate that this reaction is the most possible to undergo Model ? to give the product.The formation of C3-01 bond is greatly affected by the hydrogen(H1 and H2)transfer and the dissociation of W(CO)5.The main reason is that when the HI transfers from C3 to C2 atom,the C3 is mainly stabilized by W(CO)5,and when the W(CO)5 dissociates,the formed carbene carbon C3 is mainly stabilized by 01 atom.The rearrangement of 12 to give 14 is the rate-determining step of this reaction with an energy barrier of 31.01 kcal/mol.The presence of W(CO)5 can not only promote the HI transfer and the C3-O1 bond formation(1?6-[W]),but also be slightly favorable for the isomerization of 6-[W]into 12-[W].The NEt3 mainly takes effect in 6-[W]?12-[W]stage,in which the NEt3 mainly plays a proton-transfer bridge and a proton-adsoption roles.Secondly,the 1,2-C?C,-O?C,and-N?C migrations from?-methylene-?-silyloxy-?-amido-a-diazoacetates were investigated using density functional theory(DFT).Comparative studies on two models(Model A:1,2-migration with Rh2(esp)2;Model B:1,2-migration without Rh2(esp)2)indicate that this reaction is the most possible to undergo Model A to give the corresponding products.The selective priority of 1,2-migration reaction is from 1,2-N?C to l,2-O?C then to 1,2-C?C.This is completely in line with the experimental facts.The denitrification of 2-a to give carbonoid 4-a is the rate-determining step of this reaction with an energy barrier of 19.48 kcal/mol.The presence of Rh2(esp)2 can not only promote the denitrification of 1-a(1-a?2-a?TS3-a-?4-a),but also can change the selectivity of 1,2-migration.