Applications of Cyclometalation Five-Membered Ring Products and Intermediates as Catalytic Agents

The five-membered ring products and intermediates of cyclometalation reactions are very easily synthesized via donation from a hetero atom to a metal atom, which leads to the very high functionality of the product. This functionality is caused by the donation of the hetero atom and various types of metal atoms, halogen atom and other ligands such as alkanes, alkenes, alkynes, Cp, Cp*, aryl groups and heterocyclic compounds. These products have three types of catalytic applications: cyclometalation five-membered ring products as catalysts, cyclometalation five-membered ring intermediates as catalyst agents and cyclometalation five-membered ring intermediates with unconventional substrates and as catalyst actions. Because of the high functionality of these products, the applications of them have been increasing not only as the metathesis in the first and second generations of Hoveyda-Grubbs catalysts but also as in chiral reactions, cross-coupling reactions and polymerization reactions. The above cyclometalation products have been utilized for the production in many industrial fields such as pharmaceuticals, OLEDs, carbon dioxide utilizations, dye-sensitizer solar cells and sensors. We expect that these products would be used for the development of further new industrial products.

Circular Polymers from Ring-Opening Polymerization of Five-Membered(Thio)lactones and Derivatives

The short lifespan of most commercial plastics as disposables and the failure to adequately address the end-of-life issues of synthetic polymers have led to outrageous global plastic pollution and resource depletion.To solve the problem,one of the most effective strategies is to develop circular polymers and thus establish a new circular material economy.Polymers from ring-opening polymerization of five-membered(thio)lactones contribute greatly to this field due to their excellent material performance and recyclability.The emerging topic emphasizes on the monomer design strategies based on five-membered(thio)lactones,and compares the thermal and mechanical properties and depolymerizability of the resulting polymers with different structures.

Flavidanolides A and B from Isodon flavidus

A phytochemical investigation on Isodon flavidus led to the isolation of flavidanolide A(1),a rearranged diterpenoid featuring a six/seven/five-membered tricyclic skeleton,together with flavidanolide B(2),an uncommon heterodimeric diterpenoid consisting of a norabietane and a seco-isopimarane monomeric units.Their structures were elucidated by extensive spectroscopic data and single-crystal X-ray diffraction analyses.Their plausible biosynthetic routes were also proposed.In the bioassay,flavidanolide B was found to exhibit good inhibitory effect against lipopolysaccharide(LPS)-induced nitric oxide(NO)production in RAW264.7 cells comparable to positive control pyrrolidinedithiocarbamate ammonium(PDTC),which provided evidence for the medicinal value of I.flavidus as a folk medicine for treating inflammatory diseases.

Overview of 6π 1,5-Electrocyclization over the Past 40 Years

As an important part of pericyclic reaction,6π 1,5-electrocyclization plays an important role in organic synthesis and chemical theory.Many types of five-membered rings could be constructed via 1,5-electrocyclization with high atom economy.Some elegant works have been reported in this field in the past few decades.However,it still needs a lot of effort in further advancements of 1,5-electrocyclization.

A facile approach for the construction of the oxetane ring from 5α-acyloxy-Δ^(4(20)) - taxoids

An oxetane ring can be constructed from 5α-acyloxy-Δ4(20)-taxoids. Hie facile intramolecular acyl migration from 5- to 20-position under slightly basic conditions enabled the construction of the oxetane ring in a convenient short cut, whereas the acyl migration from 2- to 20-position left the 2-hydroxyl accessible to a later benzoylation. An unexpected five-mem-bered 4-O, 20- O sulfite ring was formed in the attempted construction of the oxetane ring with 5α-triflate as a leaving group. After the construction of the oxetane ring, treatment with strong base LiHMDS and acetyl chloride gave the expected 4-O-acetate while treatment with acetic anhydride and DMAP gave a 4-O-acetoacetate.