Transition Metal-Catalyzed Tandem Cyclization of Enediynes
|Keywords||Cyclization Enediyne Pyran Transition metal catalyzed Synthetic Methodology Tandem reaction Step reaction Concerted reaction Diethynylbenzene Multiple bonds Brominated Ester synthesis Naphthalene structure Intramolecular Type of reaction Alkyne Electrophile Terminal alkyne Steric effects Polycyclic compounds|
Transition metal catalysis has emerged as hot area in organic chemistry. Some transition metal complexes as electrophilic π lewis acids can activate C-C multiple bonds and diverse chemical transformations from alkenes and alkynes can be implemented. To explore the chemistry of enediynes under the transition metal catalysis is helpful for the discovery of new reactivity patterns, reaction mechanism as well as methodology for the construction of polycyclic heterocycles with indene or naphthalene moiety. The thesis focuses on the tandem reactions catalyzed by carbophilie metals (Au, Pd) starting from the Sonogashira products between various1,2-diethynylbenzenes and methyl2-iodobenzoates.Part I:Assembly of Indeno[1,2-c]isochromen-5(11H)-ones and Indeno[1,2-b>]pyran-2(5H)-ones via Au(I)-Catalyzed Tandem Reaction of Enediynes Bearing an Internal Carboxy GroupAn efficient approach to prepare indeno[1,2-c]isochromen-5(11H)-one and Indeno[1,2-6]pyran-2(5H)-one from enediynes has been developed and the electron effect of various substituents were examined. The tandem reaction involves C1-C5cyclization of enediynes and subsequent6-endo hydrocarboxylation. The experiments demonstrated that the tandem process was not triggered by6-endo hydrocarboxylation but initiated by the C1-C5cyclization of enediynes. The formation of the five-membered carbocycle and the six-membered heterocycle was concerted and not stepwise.Part II:Assembly of6H-Dibenzo[c,h]chromen-6-one via Pd(II)/Cu(II)-Catalyzed Tandem Reaction of Enediynes Bearing an Internal NucleophileA methodology involving construction of6H-dibenzo[c,h]chromen-6-one from enediynes bearing an internal ester group and a terminal alkyne under the catalysis of palladium chloride and copper chloride has been developed. The tandem process includes the C1-C6cyclization of enediynes and intramolecular6-endo-dig hydrocarboxylation. The preparation of chlorinated arnottin was implemented by employing the protocol. The parallel experiment showed that the C1-C5cyclization was apt to occur in the presence of copper bromide.