Recent developments of Markovnikov selective hydrofunctionalization of olefins are discussed. It is note that we realized hydrofunctionalization such as an intermolecular hydroalkoxylation, a hydrofluorination, and an intramolecular hydroamination with excellent functional group tolerance using cobalt complex, N-fluoropyridinium salt, and disiloxane. Mechanistically, this catalysis involves both carbon radical and carbocation intermediate.
In nature, enzymes can display diverse catalytic functions by exploiting structural changes in response to various external stimuli. Inspired by these flexible but well-controlled functions of enzymes, we have explored the conformationally flexible organocatalysts, which enable to construct enantiomerically distinct chiral environments with a single chiral source. Here we describe recent advances in the development of dynamic asymmetric organocatalysis, including retro-free, enantiodivergent, entropy-controlled organocatalysis, and programmed-organocascade, in which a single asymmetric organocatalyst can afford different functional outcomes by timely tuning the reaction conditions. Special emphasis is placed on key requirements to attain high selectivity and on functional switching by exploiting the structural flexibility of our organocatalysts.
I herein describe iridium- and rhodium-catalyzed C(sp3)-H silylation at the benzylic position and the position adjacent to a nitrogen atom by the aid of a nitrogen directing group. The silylated products could be further carboxylated with carbon dioxide (1 atm of CO2) under fluoride-mediated conditions, giving carboxylic acid derivatives in high yields. It should be a formal carboxylation of C(sp3)-H bonds triggered by metal-catalyzed C-H silylation. We also developed a novel triborylation reaction of terminal C(sp3)-H bonds (2-ethylpyridine derivatives). The obtained triborylated compounds were successfully converted into carboxylic acids by using either CsF under a CO2 atmosphere or H2O2 in the presence of TsOH·H2O.
2,2-Disubstituted 1,2-dihydro-3H-indol-3-ones are useful synthetic intermediates for natural products. Therefore, its preparation in a concise manner is highly desirable. Recently, we reported a methodology for the preparation of 2,2-disubstituted 1,2-dihydro-3H-indol-3-ones through the successive oxidation of indoles and Mannich-type reaction of 2-hydroxy-1,2-dihydro-3H-indol-3-ones with various carbon nucleophiles. Using this method, we accomplished the total synthesis of (±)-hinckdentine A. The synthesis featured seven-membered lactam formation by Murahashi’s Ru catalyst and the selective tri-bromination of aromatic ring. Also, we performed the synthesis of isatisine A framework. In this research, we found an intriguing reaction in which nucleophiles are introduced at the C-2 position of 3H-indol-3-one via activation with TFAA. Towards the total synthesis of leuconoxine, ring construction steps featuring the N-acyliminium mediated intramolecular piperidine cyclization and the one-step pyrrolidone formation using Bestmann’s ylide are achieved successfully. Utilization of a chiral phosphoric acid catalyst (VAPOL PA), the asymmetric desymmetrization of prochiral diester produced highly-enantioenriched lactam in excellent yield. Using this strategy, we accomplished the asymmetric total synthesis of (−)-leuconoxine.
Azaporphyrinoids, such as phthalocyanines (Pcs), tetraazaporphyrins (TAPs), and tetrabenzotriazacorroles (TBCs) are some of the most well-known and successful artificial dyes and pigments in modern material chemistry. In this article, on modifying optical properties of azaporphyrins, we have proposed a novel “π electron-unmodified” approach by utilizing the unique properties of the phosphorus(V) ion with simple macrocyclic ligands. Although the azaporphyrin phosphorus(V) complexes could be synthesized via simple synthetic procedures, they revealed unique optical properties not seen in other metalloazaporphyrinoids reported to date, such as intense absorption and fluorescence bands beyond 1,000 nm, broad absorption bands across the entire UV-vis region, and high singlet oxygen quantum yields. The combination of peripheral substituents and theoretical calculations was effective for the rational design of optical properties in the UV-vis-near-IR region, which is also demonstrated. The practical synthesis, purification, and characterization of azaporphyrins have also been described for general organic synthetic chemists.
Complexation of an arene to a low-valent metal carbonyl, such as Cr(CO)3, transfers electron density from the aromatic ring to the metal tricarbonyl moiety. As a result, the acidity of the aromatic ring as well as of the benzylic position is enhanced. Recently, several groups have developed catalytic reactions using a (π-arene)chromium complex, which is enhanced the reactivity of the arene by complexation.
Hypervalent iodine alkynylating reagents enable electrophilic alkynylation of various nucleophiles. Their unique umpolung reactivity is expedient to access heteroatom-substituted alkynes which have been challenging to synthesize. Alkynylation of thiols with R-EBX is remarkably efficient and practical to provide the corresponding thioalkynes with excellent chemoselectivity. In addition, the reaction mechanism was examined using DFT calculations.
Hydrometalation of alkenes with transition-metal hydrides (M-H) represents an important step in transition-metal-catalyzed transformations. Most of the reactions proceeded in anti-Markovnikov fashion to afford the corresponding adducts with high regioselectivity. On the other hand, the different types of reactions of alkenes with transition-metal hydrides, such as Co-H, Mn-H, and Fe-H, have been developed, which gave the corresponding organic radical species. Recently, a number of transformation reactions of the organic radical species catalyzed by transition-metal hydride complexes have been reported. Herein, the formation of organic radical species by the reaction of transition-metal hydrides with alkenes and their recent application to practical organic synthesis are highlighted.