Recent progress in catalytic reactions via copper-acetylide complexes as key intermediates is reviewed from the viewpoint of organic synthesis. A variety of novel catalytic reactions such as cross-coupling reactions, addition reactions, and cycloaddition reactions using copper-acetylide complexes as carbon sources have been developed. Copper complexes bearing an optically active ligand promote various asymmetric transformations such as propargylic substitution reactions of propargylic esters and ring-opening reactions of ethynyl epoxides, where copper-allenylidene complexes work as key and common intermediates.
Polyhedral metal-main group clusters have attracted much attention, because of their structures and properties such as electron transfer and emission as well as a catalyst in organic syntheses. In this paper, we wish to report our recent results concerning the polyhedral platinum-silyl clusters. The reactions of zero-valent platinum complex bearing phosphine ligands with disilanes afforded the trigonal bipyramidal Pt3Si2 or octahedral Pt4Si2 clusters. Use of a sterically small disilane reduces the repulsion between the disilane and the phosphine ligand to induce the formation of higher dimensionally clusters. Each of the platinum-silyl clusters has a polyhedral skeletal structure compressed to Si-Si alignment with long Pt-Pt and short Si-Si distances, compared with those of the platinum clusters including other main group elements such as S, Se, and Ga. The liberation and rebinding of the phosphine ligand regulate a 1,2-migration on the platinum center in the formation process of clusters.
The basic utility and application of ruthenium tetroxide (RuO4) oxidation of N-acyl amines and their related compounds including optically active substrates are described. The oxidation of acyclic and cyclic N-acyl amines proceeded smoothly at room temperature by active RuO4, which was generated in situ from a catalytic amount of ruthenium dioxide (RuO2·xH2O) and an excess of 10% aqueous sodium metaperiodate (NaIO4) in a double layer system of ethyl acetate-water to afford the corresponding imides in good to excellent yields. Cyclic ene-carbamates were oxidized at their carbon-carbon double bond to produce ω-(N-formylamino)carboxylic acids as the major products. The conventional double layer system of the reaction medium was changed to a single layer aqueous system containing tert-butanol, in which oxidation directly cleaved the endo-cyclic C-N bond to give ω-amino acids as the sole open-ring products. The syntheses of baclofen, lycoperdic acid, optically active pyrrolidine-3-phosphonic acids and L-carnitine were accomplished using RuO4 oxidation as the key step.
Chlorosulfolipids (CSLs) represent an unusual family of natural products that were first isolated from the freshwater alga Ochromonas danica in the 1960s. They have drawn considerable attention as substances of toxicological concern, because some of them display modest cytotoxic activity and are associated with seafood poisoning. CSLs are unique in featuring hydrocarbon framework which possess chlorine-substituted multiple stereogenic centers. Due to the unprecedented structure and interesting biological activity of CSLs, this fascinating class of natural products has recently garnered interest as targets of total synthesis and inspired methodology for stereoselective chlorination. In 2009, Carreira accomplished the total synthesis of hexachlorosulfolipid. After this total synthesis, other three groups including our group have achieved total syntheses of CSLs: Malhamensilipin A and danicalipin A by Vanderwal, hexachlorosulfolipid and danicalipin A by Yoshimitsu and Tanaka, and danicalipin A by authors. This review deals with these total syntheses of CSLs, focusing the development of synthetic methods to stereoselectively incorporate acyclic polychlorinated arrays into hydrocarbon skeletons of CSLs.
An intriguing umpolung of the reactivity of imines possessing electron-withdrawing groups was observed. For example, N-alkylation/coupling reaction of the imines derived from glyoxylates was conducted with dialkylaluminum chloride in acetonitrile to give N-monoalkylated 1,2-diamines in good yields. On treatment of various α-imino esters with organoaluminum reagents and allyltributhyltin in the presence of benzoyl peroxide (BPO), the tandem reaction proceeded to give the N-alkylation/C-allylation products in good yields. Diethyl 2-[N-(p-methoxyphenyl)imino]malonate underwent amination reactions with alkyl Grignard reagents to give N-alkylation products in good yields. The obtained N-alkylation products were readily converted into N-alkyl-p-anisidines by the oxidative removal of the malonate moiety. In order to enhance the reactivity of imines, an iminium salt was prepared using the oxidation of amino ketene silyl acetal with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and the subsequent nucleophilic addition to this iminium species proceeded to afford α-amino esters in good yields.
Dendrimers containing rigid conjugated backbones were prepared by a convergent method where the attachment of dendritic branches and the extension of phenylene-ethynylene units were alternatively manipulated on the structure of AB2 substituted phenylacetylene in a combination with Suzuki-Miyaura and Sonogashira cross-coupling reactions. These dendrimer structures were applied for the construction of several light-harvesting antennas and charge-separating systems. The conjugated network inside the dendritic structure was shown to play an important role as a mediator in both the photoinduced energy- and electron-transfer processes. In addition, we describe a novel methodology for the stepwise construction of shape-persistent assemblies using the dendrimers with conjugated backbones as the key modular building blocks. These examples demonstrate advantage of the dendrimer with conjugated backbones for the construction of nanoscale molecular devices such as artificial photosynthetic systems.
“Click Chemistry” is a chemical concept proposed by Prof. Sharpless in 2001. Notable advantages of click reactions are their high level of efficiency, stereospecificity, atom economy, and functionality tolerances. A large number of examples have been reported in this decade due to the usefulness of click reactions. While Huisgen reaction is the most representative example in this field, they have gradually been expanded to a variety of reactions and utilized for bioconjugations and peptide syntheses.
Palladium-catalyzed difunctionalization of alkenes, which forms two new σ-bonds in a single step, is attractive for synthesizing complex molecules. This short review summarizes 1,1-difunctionalization reactions of terminal alkenes, which have been emerging as a new tool that complements the conventional 1,2-difunctionalization.
Pseudolaric acids A and B are diterpene acids isolated from the bark of Pseudolarix kaempferi Gordon (pinaceae). The unique tricyclic framework of pseudolaric acids as well as their remarkable biological properties has drawn enormous attention of the chemists. In this short review, three total syntheses of pseudolaric acids A and B are described with focusing on the construction of their tricyclic core.