Investigations On Palladium Catalyst Systems And Reaction Mechanism For Four-membered-ring-strain Drived Ring-opening And Ring Expansion Transformations

Cyclobutanes usually serve as a privileged ring structures with high ring strain and constitute the central core of a variety of organic chemicals,and recent investigations demonstrated that cyclobutanes could be activated by transition metal catalysts to form a metal cyclopentane intermediates,followed by the ring expansions reactions at the position of C-C bond or C-Si bond with other organic partners.However,it often encounters difficulty in controlling regio-and stereo-selectivity of these transformations.In this thesis,based on the theoretical study of C-C bonds and C-Si bonds cleavage,the studies on tension-driven ring-opening and ring-expanding dual functionalization of cyclopropenes with benzosilacyclobutanes was carried out with the aid of palladium catalysis.In addition,the reaction mechanism of cyclobutanone compounds was investigated and verified,and the scientific findings were obtained as following:1.A novel and unusual palladium-catalyzed [4+2] annulation of cyclopropenes with benzosilacyclobutanes is reported.This reaction was completed through chemoselective Si-C bond activation synergized with ring expansion/insertion of cyclopropenes for the formation of new C-C and Si-C bonds.An array of newly elusive bicyclic skeleton with high strain,sila-bicyclo[4.1.0] heptanes,was formed with good yields and excellent diastereoselectivity under mild conditions.An asymmetric version employing chiral phosphoramidite ligand have been explored to furnish this challenged reaction to a variety of chiral bicyclic sila-heterocycle derivatives with good enantioselectivity(up to 95.5:4.5 er).In addition,the downstream transformations of sila-bicyclo[4.1.0] heptanes was carried out to synthesize a series of cyclopropane compounds with high diastereoselectivity in the presence of TBAF.2.For the novel palladium-catalyzed ring expansion reaction of cyclobutanones with aromatic iodine structure to achieve a highly selective C-C and C-I σ bond cross-exchange reaction,we carried out DFT calculations to clarify the reaction mechanism.The experimental results supported that a reaction path with hypervalenpalladium intermediate was possibly active species.And the relationship between the construction of the quaternary stereocenters and the steric effect of the chiral ligand was studied and explored in detail,in which the chiral ligand played crucial role in this reaction.In summary,a novel palladium-catalyzed dual functionalization of cyclopropenes with benzosilacyclobutanes has been established.And taking advantage of the high reactivity of the four-membered cyclobutanes,an array of newly elusive bicyclic skeleton with high strain,sila-bicyclo[4.1.0]heptanes,was achieved under mild conditions.