Olefin metathesis is established as a remarkably valuable synthetic tool in current organic chemistry. We report here total synthesis of natural products using sequential olefin metathesis reactions. The one-pot ring-opening/cross/ring-closing metathesis (ROM/CM/RCM) reaction has been developed, allowing for the concise construction of the oxygen-bridged 1,3-cyclooctadiene framework from an oxanorbornene derivative and 1,3-butadiene. The ROM/CM/RCM product was converted into (+)-mycoepoxydiene, (−)-1893A, and (+)-1893B. Furthermore, the ring-opening/ring-closing metathesis (ROM/RCM) of cyclobutenecarboxylate derivatives has been developed as a novel method for access to γ-butenolides. The enantioselective total synthesis of (+)-clavilactone A and (−)-clavilactone B was achieved by the use of this reaction (ROM/RCM).
N-Sulfonyl-1,2,3-triazoles are readily prepared by a copper(I)-catalyzed 1,3-dipolar cycloaddition reaction of terminal alkynes with sulfonyl azides. Their ring-chain tautomerization generates α-imino diazo compounds, although the equilibrium lies far to the triazole form in general. Transition metal catalysts, especially rhodium(II) carboxylate dimers, can efficiently trap the transient α-imino diazo compounds to give α-imino metal carbene complexes with the extrusion of molecular nitrogen. These metal carbene complexes share many features with the well-known α-oxo metal carbene complexes derived from α-dizao carbonyl compounds. However, in some cases, the presence of the nucleophilic imino nitrogen endows their unique reactivity depending on the reactants as well as the catalysts. In this article, we describe nickel(0) and rhodium(II)-catalyzed inter- and intramolecular reactions of N-sulfonyl-1,2,3-triazoles with various types of reactants such as carbon, oxygen, and sulfur nucleophiles, which provide a facile method for the synthesis of nitrogen-containing compounds. These reactions are successfully applied to all-in one-pot reactions starting from terminal alkynes.
Stereoselective addition reactions of in situ generated XX’ (IBr, BrCl) and HX (X =Cl, Br, I) to alkynes are described. The in situ XX’ were found to effectively occur from mixing up of commercially available halotrimethylsilane (TMSX) with N-halosuccinimide (NX’S). The in situ BrCl effectively bonded to silylethynylarenes in complete syn-fashion, and the in situ IBr reacted with internal aliphatic alkynes and ynamides in anti-mode; these afforded perfect formation of single isomers. The resultant bis-halogenated alkenes can be reasonably multi-tunable templates for synthesis of differentially all-carbon tetrasubstituted olefins. In a similar vein, the in situ HX generated from TMSX and H2O undertook stereoselective addition of alkynes, which gave synthetically mono-halogenated scaffolds for preparing trisubstitued olefins and disubstituted exo-methylenes. It thus provided a potentially diverse scaffold for differently poly-substituted olefins.
2-Azahypoxanthine (AHX, 1) and imidazole-4-carboxamide (ICA, 2) were isolated from a fairy-ring forming fungus Lepista sordida. AHX was converted into a metabolite, 2-aza-8-oxohypoxanthine (AOH, 3), in plants. Afterward, it turned out that these three compounds, fairy chemicals (FSc), endogenously exist in plants and are biosynthesized via a new purine metabolic pathway. Furthermore, FCs increased the yields of rice, wheat and other crops in the field experiments.
Large aromatic molecules such as polyacenes and polycyclic aromatic hydrocarbons are regarded as promising materials for organic electronic devices. However, it is normally difficult to synthesize such large aromatic molecules because of the low solubility and stability. On the other hand, we have developed thermal and photochemical precursor methods to overcome these problems. Briefly, bicyclo [2.2.2] octadiene-fused acenes can be converted to the corresponding acenes by the thermally induced retro-Diels-Alder reaction, while α-diketone-type precursors can be converted simply by photoirradiation. Importantly, these precursor molecules are often more soluble and stable than the corresponding post conversion compounds, indicating that this methodology enables us to prepare solution-processed organic electronic devices. This paper highlights the design and synthesis of large aromatic compounds and demonstrates a new way for multicomponent layer-by-layer preparation of organic semiconducting films through thermal and photochemical precursor methods.
One of the modern medicinal chemistry methods is kinetic target-guided synthesis, where fragment molecules are interacted with a target protein and those in close proximity on the protein spontaneously cross-link by forming a covalent bond. The reactions, which is applicable to the kinetic target-guided synthesis proceed in water and are required no additional reagent. Here, several examples of kinetic target-guided synthesis are described.