Iron-or Copper-Catalyzed Intramolecular Cyclization Reactions Of Alkynes

Transition metal-catalyzed intramolecular cyclization of alkynes has attracted significant interest because of their synthetic utility in the realm of furnishing cyclic derivatives, which are valuable synthetic intermediates, as well as important structural units in numerous natural products and pharmaceutical molecules. Despite considerable progress in this field, the development of mild, efficient, economical cyclization routes using inexpensive catalytic materials to construct new, complex compounds remains a important challenge. The dissertation mainly discusses iron or copper-catalyzed intramolecular cyclization reactions of alkynes. The main contents are included:(1) A novel intramolecular annulation strategy to construct substituted naphthalen-1-ols and anthracen-1-ol, using an economical and environmentally-benign iron catalyst is described. It was found that base played an important role in this reaction, and KOAc was the most effective for the reaction. This new atom-economically intramolecular annulation of 1-(2-alkynylphenoxy)-propan-2-ones includes dual C-H functionalizations and one C-O bond cleavage transformation.(2) Numerous functional indeno[1,2-c]chromenes and 5H-naphtho [1,2-c] chromenes are readily synthesized from 2-(2-(ethynyl) phenoxy)-1-arylethanones by an iron-mediated tandem annulation strategy. In the presence of PhMe and FeCl3, a variety of 2-(2-(ethynyl) phenoxy)-1-arylethanones smoothly underwent electrophilic addition of a ketone to an alkyne and annulation tandem reaction, providing the corresponding products in moderate to excellent yields. Importantly, a halide is introduced into the products by a ring-opening process among the [3+3] annulation of alkynylcyclopropanes, which makes the methodology more attractive for organic synthesis.(3) A novel and efficient protocol for the synthesis of substituted 1,4-naphthoquinones has been demonstrated via the CuCl2-catalyzed oxidative cyclization of 1,6-enynes. The CuCl2/O2/Ce2(SO4)4 catalytic system provided the corresponding oxidative cyclization products in moderate to excellent yields with a wide range of substrates compatibility. This work is the first to disclose a copper-catalyzed enyne oxidative cyclization for constructing 1,4-naphthoquinones by the incorporation of two oxygen atoms into the organic framework from molecular oxygen and water. Importantly, using O2 as both the terminal oxidant and a reactant expanded the application in synthetic organic chemistry. Moreover, the mechanism was discussed according to the 18O-labeling experiments and the results presented.(4) A novel and efficient electrophilic ipso-halocyclization of N-arylpropynamides with polyfluoroalkyl alcohols has been developed for the synthesis of 8-(polyfluoroalkoxy)-1-azaspiro[4.5]deca-3,6,9-trien-2-ones. In the presence of N-halosuccinimides (NXS), a variety of N-arylpropynamides underwent an electrophilic jpso-halocyclization reaction with polyfluoroalkyl alcohols to afford the corresponding 8-(polyfluoroalkoxy)spiro[4.5]trienes in moderate to good yields. It is noteworthy that molecular sieves can improve the yield.(5) A general and mild method for the construction of functional ized 2-(1H-indol-3-yl)-2-amino-carbonyl compounds was achieved, which represents the first example of direct a-arylation of a-amino carbonyl compounds with indoles using the visible light photoredox catalysis strategy. In the presence of Ru(bpy)3Cl2, O2 and 5 W blue LEDs light, treatment of indoles with 1-phenyl-2-(phenylamino)ethanones afforded corresponding products in moderate to excellent yields.