Simulation of the functions of cytochrome P-450 with transition-metal catalysts such as ruthenium complex catalysts led to the discovery of biomimetic catalytic oxidation reactions of various substrates such as amines, amides, olefins, alcohols, phenols, ketones and hydrocarbons. These catalytic reactions are practical and highly useful for synthesis of biologically active compounds, which include cortisone acetate and adriamicine acetate. Importantly, (1R, 3S) -3- [1'- (t-butyldimethylsilyloxy) ethyl] azetidi-2-one can be converted to the corresponding 4-acetoxyazetidinone, which is a versatile and key intermediate for the synthesis of carbapenem antibiotics, with extremely high diastereoselectivity (99% yield, 99% de). This becomes important industrial process. The oxidations of amines and amides provide highly useful 4 methods for introduction of a substituent at the α-position of amines by the oxidation of amines and amides and subsequent treatment with nucleophiles.
Singlet biradicals are key intermediates in processes involving homolytic bond-cleavages and bond formations. In general, the reactive intermediates are quite short-lived, and thus, largely elusive. To understand experimentally the reactivity, it is dispensable to pull down the singlet state below the triplet state and elongate the lifetime of singlet states. This paper describes that (1) substituent and atom effects on the ground state spin-multiplicity of cyclopentane-1, 3-diyls, (2) generation of long-lived singlet 2, 2-dialkoxycyclopentane-1, 3-diyls, and (3) the intermolecular reactivity of the singlet biradicals.
Novel structural modification, i.e., annelation of bicyclo [2.2.2] octene units, for stabilizing unstable cationic π-electron systems has been developed. The rigid alkyl substituent stabilizes the cationic species due to cumulative weak thermodynamic effects and steric protection, and therefore it does not distort the intrinsic electronic structure of the π-systems. By applying this structural modification, the first isolation and X-ray structural analysis of various radical cation and dication salts and the generation and first NMR observation of quite unstable cationic π-conjugated systems were realized. Combined with the results of theoretical calculations, the electronic properties of these cationic species were investigated. These involve aromaticity of cationic π-conjugated systems including sulfur and silicon atom (s), relationship between the molecular orbital and structural changes upon one electron oxidation, and electronic structure in oxidized states of π-conjugated oligomers.
Squaric acid belongs to a class of oxocarbons and exhibits unique physicochemical properties, e.g., strong acidity, aromaticity, strained ring, electron deficiency, and metal chelating ability. Squaric acid has received considerable attention as a carboxylic acid mimic in medicinal chemistry, a novel chromophore in material science, a new chelator in inorganic chemistry, and a building block of quinones, triquinanes, cyclopentenones, and furanones in organic synthesis. Recently, squaric acid diesters are employed for a variety of applications in scientific fields as a linker to construct novel bioconjugate molecules. This review will describes recent progress on the use of squaric acid focused on bioorganic research.
This review article describes recent developments in the studies of syntheses, structures, and properties of functional fullerene derivatives, including metal-fullerene complexes, hoop-shaped cyclic π-electron conjugated systems, and shuttlecock-shaped fullerene-containing liquid crystalline molecules. Electrochemistry, photophysics, luminescence, and supramolecular behaviors of these materials from the point of view of structural chemistry, are described.
Carbon-carbon bond-forming reactions of allylic organometals have been recognized as one of the most fundamental means in organic synthesis, and a number of applications for the synthesis of biologically active molecules have been reported. We have reported the carbon-carbon bond-forming reactions by the use of the allylic and related zirconium species as reactive intermediates. These zirconium species can be generated by treating allylic ethers with zirconocene-butene complex (“Cp2Zr”) through the formation of zirconacyclopropane and the following β-elimination of the alkoxy group. This process was found to be applicable to generate the γ, γ-dialkoxyallylic zirconium species 1 from orthoacrylate derivative. Zirconium species 1 possibly has three reactive sites : One is the γ-position as a typical allyl metal species, the other is the β-position followed by the α-position initiated by nucleophilic character of ketene dialkylacetal moiety and the third one is regioselective coupling reaction at the α-position. Thus, γ, γ-dialkoxyallylic zirconium species 1 can be conveniently prepared by the reaction of triethyl orthoacrylate with “Cp2Zr”. Without an additive, 1 itself reacts with aldehydes and ketones at the γ-position to afford the gem-diethoxy homoallylic alcohol derivatives. Under Lewis acid promoted conditions, this zirconium species 1 reacts with a variety of carbonyl compounds selectively at the β-position in the first step, followed by the cyclopropanation or cyclobutanation reaction to afford the corresponding products mainly depending on electronic nature of substrates or reaction conditions. In the presence of CuCN, reaction of 1 with allylic phosphates proceeded at the α-position of 1 in a highly SN2'-selective manner to give the 5-alkenoates.
Multicomponent Reactions have attracted considerable attention with respect to the needs to improve the capability to synthesize molecules in more facile and efficient as well as economy ways. Although a large number of MCRs have been reported from the late of 18 th century, the initial disclosure of catalytic asymmetric version was made only several years ago. In this short review, several recent examples of catalytic asymmetric α-aminoalkylation are introduced.