Enantioselective vanadium catalysts provide new and powerful tools for the efficient preparation of optically active molecules. Over the past few decades, vanadium catalysts have been utilized in various asymmetric reactions, especially in the field of Lewis acid-based chemistry and redox chemistry. So far, we have developed a dinuclear vanadium(V) complex, which can catalyze the oxidative coupling of 2-naphthols to give the corresponding 1,1’-bi-2-naphthol (BINOL) derivatives through a dual activation mechanism. In the coupling reaction, the two vanadium metals in the chiral complex activate two molecules of 2-naphthol simultaneously achieving a high reaction rate with high enantiocontrol (up to 97% ee). This review will mainly focus on the applications of dinuclear vanadium complexes to oxidative couplings of polycyclic phenols and enantioselective synthesis of oxahelicenes.

We developed several naphthalene oligomers with contiguous chiral axes as chiroptical dyes. RS-alternating oligomers with the 2,2’-methylenedioxy bridges take a V-shaped conformation with a notably extensive conjugation in the rod direction, leading to high fluorescence in solution and in the solid state (Φ_FL,solution=0.64 and Φ_FL,solid=0.13 for an octamer). Theoretical studies indicated that the dihedral angles of naphthalene rings were held steady 48—49°, and both the HOMO and LUMO were spread throughout the molecule. It should be noted that the bridged(R,R,R,R,R,R,R)-naphthalene octamer showed more intense fluorescence (FL) and circularly polarized luminescence (CPL) (Φ_FL,solution=0.90, g_lum,solution=+2.2×10⁻³, Φ_FL,solid=0.22, and g_lum,solid=+7.0×10⁻³). The high Φ_FL and g_lum values were due to the rigidity. Moreover, the octamer molecules were incapable of forming efficiently stacked structures due to the non-planar conformation, which led to a high Φ_{FL, solid} value in the solid state. A(R,R,R)-naphthalene tetramer possessing eight pyrenes displayed intense excimer-FL and CPL (Φ_FL,solution=0.25, g_lum,solution=+0.034, Φ_FL,solid=0.28, and g_lum,solid=+5.3×10⁻³). Pyrenes densely connected to a naphthalene tetramer via ester linkers were conformationally rigid with right-handed chirality and were important for obtaining strong CPL.

Naturally-occurring B₁₂(cobalamin)-dependent enzymes catalyze various molecular transformations that are of particular interest from the viewpoint of biological chemistry as well as synthetic organic chemistry. As bioorganometallic compounds are considered as intermediate for B₁₂-dependent reactions, those were utilized as catalysts for various molecular transformations. Using the unique property of the B₁₂ compound, various catalytic reactions have been developed using its model complex. Electroorganic syntheses mediated by the B₁₂ complex have been developed as green molecular transformations. The redox active B₁₂ complex shows a unique catalysis in organic synthesis such as the dechlorination of organic halides and the radical mediated isomerization reactions. The B₁₂ complex-photosensitizer composites have also become a green and efficient catalyst for molecular transformations. The B₁₂-dependent enzymes mimic reactions catalytically occurring using the B₁₂ complex-photosensitizer composites. In addition to the B₁₂ mimic reaction, novel bioinspired reactions were also developed, such as hydrogen production or alkene and alkyne reductions, and the cobalt-hydrogen complex was considered as a putative intermediate of the reactions.

This review describes synthetic methods that have brought remarkable increase of synthesizable ellagitannins. Acquisition of capability to enable syntheses of all ellagitannins, which are more than 1,000 characterized natural products and their analogues, would contribute to development of understanding structure-activity relationship. The two major reasons diversifying the structures of ellagitannins are the presence of the hexahydroxydiphenoyl group and the C-O digallates, each of which arises through formation of a C-C or a C-O bond between two galloyl groups. To increase the number of synthesizable ellagitannins, establishment of methods for synthesizing these two components and for assembling the components to construct ellagitannin molecules are essential. Three focuses here are methods for synthesizing (1) the hexahydroxydiphenoyl group, (2) glucose derivatives with hexahydroxydiphenoyl bridges, and (3) the C-O digallates. In addition, several applications of these methods for total syntheses of ellagitannins are exemplified.

Morphinan alkaloids, such as morphine, codeine, heroin, and thebaine, which are called opioids, are pharmacologically important compounds and widely known to express a variety of pharmacological action by acting on µ, δ, and κ opioid receptors (MOR, DOR, and KOR). Naltrexone, which is one of the commercially available 4,5-epoxymorphinan alkaloids, is a drug mainly used to manage alcohol dependence and opioid dependence. From a viewpoint of pharmacology, naltrexone is categorized as a MOR antagonist. On the other hand, from a viewpoint of organic chemistry, it has a wealth of functional groups and four consecutive asymmetric centers in the single molecule, and thus, naltrexone or its derivatives show a characteristic of chemical reactivity. In this article, unique reactions of morphinan skeletons based on our recent research in medicinal chemistry were described. In the first chapter, we focused on the effects of the hydroxy group at the C14 position and the tetrahydrofuran-ring (4,5-epoxy-ring, E-ring) in the naltrexone derivatives to lead the abnormal reactions. In the second chapter, we described the synthetic transformations of naltrexone into (−)-galanthamine and (−)-homogalanthamine. This article would hopefully be useful information for both organic synthetic chemists and medicinal chemists.

Cyclopropanes represent an important class of organic compounds due to their synthetic utility and their widespread occurrence in nature. In addition, the rigid conformation of cyclopropanes as the smallest conceivable [C₃] ring compound can be exploited in stereo-controlled syntheses. Especially donor-acceptor (D-A) cyclopropanes have attracted considerable attention due to recent synthetic developments. This article describes the ring-opening cyclization, homo-Nazarov cyclization, oxy-homo-Michael reaction, 1,5-addition and reductive ring-opening reaction of enantioenriched donor-acceptor cyclopropanes. In addition, a couple of asymmetric total synthesis of bioactive lignans using a couple of these reactions as key steps. Namely, we achieved the asymmetric total synthesis of tupichilignan A using the highly stereoselective Cu(OTf)₂-catalyzed oxy-homo-Michael (OHM) addition of alcohols into bicyclic donor-acceptor cyclopropanes as a key step. Moreover, Cu-catalyzed 1,5-addtion of Grignard reagent instead of alcohols into the enantioenriched donor-acceptor cyclopropanes also proceeded with high regio- and stereoselectivity. In addition, we reported the hydrogenolysis (reductive ring-opening) of D-A cyclopropanes and its application for the total synthesis of yatein. Beside the intermolecular reaction, we verify the reaction mechanism of ring-opening cyclization and homo-Nazarov cyclization of D-A cyclopropanes. Based on the mechanistic point, this paper describes the highly stereoselective synthetic methods utilizing (i) the intermolecular addition of nucleophiles to enantioenriched D-A cyclopropanes via S_N2 pathway and (ii) the intramolecular chiral transfer Friedel-Crafts alkylation via S_N1 pathway after cyclopropane-opening.

On treatment with a cationic Pd(II) catalyst in the presence of BF₃·OEt₂, 1,1-difluoroalkenes and 1,1,2-trifluoroalkenes underwent Friedel-Crafts-type ring closures (direct activation) to afford pinpoint-monofluorinated and pinpoint-vic-difluorinated phenacenes (F-phenacenes), respectively. Treatment of 1,1-difluoroallenes with an InBr₃ catalyst facilitated domino cyclization (indirect activation) leading to the synthesis of F-phenacenes and related F-PAHs. Using the formed F-PAH library, the physical properties of these compounds were investigated. Notably, the HOMO-LUMO energy gaps of F-picenes, consisting of five benzene rings, were smaller than that of the corresponding fluorine-free picene by 0.02-0.26 eV. The HOMO energy levels of F-picenes were lowered by 0.10-0.22 eV, leading to enhanced resistance of these materials to aerial oxidation. 5-Fluoropicene and 13-fluoropicene exhibited p-type semiconducting behavior [5-fluoropicene: 2.8×10⁻⁵ cm²/Vs (vacuum deposition); 13-fluoropicene: 6.6×10⁻² cm²/Vs(vacuum deposition), 1.3×10⁻⁴ cm²/Vs (spin casting)]. The introduction of fluorine substituent(s) into picenes increased their solubilities in organic solvents, which was best exemplified by the much higher solubilities of 6-fluoropicene (5.3 wt%), 6,7-difluoropicene (5.3 wt%), and 13-fluoropicene (3.1 wt%) in THF, compared to that of picene (0.20 wt%)。

Recently, introduction of fluorine atoms to pharmaceuticals, agrochemicals and materials has attracted much attention. Although a lot of fluorination reactions of carbonyl compounds have been developed, the number of β-fluorinations of carbonyl compounds is limited. Generally, activation of C-H bond at β-position of carbonyl group is not so easy and synthesis of β-fluorocarbonyl compounds is challenging. Herein, recent reports for syntheses of β-fluorocarbonyl compounds using transition metal catalysis are highlighted.