Recently copolymers containing cyclic hydrocarbon structure are paid great attention for its high transparency, heat resistance, and low dielectric constants. One of the most promising monomer to synthesize these kinds of polymers is norbornene, which is polymerized by either of ring-opening metathesis polymerization or coordinated insertion polymerization. In our contribution, we developed a living coordination polymerization system using ansa-fluorenylamidotitanium complex as a catalyst and applied it to the norbornene homopolymerization and random copolymerization with ethylene, propylene, 1-alkene and styrene. Block copolymerizations with propylene, 1-octene, norbornene and methyl methacrylate are also described.
Development of biofunctional molecules is an essential research field in the progress of chemical biology and medicinal chemistry. Natural products show various biological activities, thus they are expected to be lead compounds of novel-type of drugs. Also, natural products with a novel mechanism of action are important tools for study of biological phenomena. We have achieved the total synthesis of (−)-13-oxyingenol. This approach is highlighted by ring-closing olefin metathesis for the construction of an inside-outside framework and Mislow-Evans-type[2,3]-sigmatropic rearrangement for the introduction of a hydroxy group at C5. On the other hand, we have synthesized a hybrid molecule, consisting of the macrolactone part in aplyronine A and the side chain part in mycalolide B, by using two asymmetric Ni/Cr-mediated reaction and an intramolecular Ni/Cr-mediated macrocyclization as the key steps and have biologically evaluated this compound.
Highly selective organic transformation reactions using halogen Lewis acids are described here. 2-Iodobenzenesulfonic acid has been found to be effective as a precursor of iodine(V) catalyst for the selective oxidation of alcohols and phenols in the presence of Oxone® as a cooxidant. C2-Symmetric iodoarenes bearing conformationally flexible chiral secondary amido groups have been developed as precursors of iodine(III) catalysts for the enantioselective dearomatization of 1-hydroxynaphthyl carboxylic acids and hydroxyphenyl carboxylic acids in the presence of m-chloroperbenzoic acid (mCPBA) as a cooxidant. Chiral quaternary ammonium iodide has been developed as a precursor of iodine(I) catalyst for the enantioselective dehydrogenative carbon-oxygen coupling reaction in the presence of hydrogen peroxide or tert-butyl hydroperoxide (TBHP). Several chiral phosphorous compounds have been developed as chiral nucleophilic base catalysts for the biomimetic enantioselective iodocyclization, bromocyclzation, and protocyclization of polyprenoids. These phosphorous compounds activate N-halosuccinimides (NIS, NBS) and sulfonic acids as halonium salts and protic salts, respectively.
Porphyrin is a representative functional molecule, which consists of four pyrrole units linked by four carbon atoms with an 18π aromatic character. Most of porphyrin syntheses rely on acid-catalyzed condensation of pyrrole with aldehydes followed by oxidation, which are low-yielding in many cases. To establish more effective porphyrin synthesis, we have devoted our effort to combine porphyrin chemistry and modern organic synthesis through transition metal-mediated reactions. In this article, we focus on synthesis of novel porphyrin analogues through coupling of dipyrrin precursors. The metal-templated strategy using dipyrrin metal complexes was found to be quite efficient to construct porphyrin-like cyclic π-conjugated systems consisting of the dipyrrin unit, which exhibit intriguing optical and electronic properties.
Bis(trifluoromethylsulfonyl)methyl (Tf2CH; Tf=SO2CF3) group is an appealing acidic functionality for development of novel organocatalysts. It has been reported that some compounds bearing Tf2CH functionality show notably strong acidity in both solution and gas phases, although the catalysis of such carbon acids has not been defined for a long time. On the other hand, we recently found that 1,1,3,3-tetrakis(trifluoromethylsulfonyl)propane (Tf2CHCH2CHTf2) performs as an excellent catalyst for several carbon-carbon bond forming reactions using silicon enolates. Furthermore, as an effective strategy to prepare a novel type of carbon acid catalysts, we reported that Tf2CHCH2CHTf2 can be successfully used as a suitable reagent for incorporating Tf2CH functionality to neutral nucleophiles. On the basis of this strategy, multiple carbon acid catalysts were developed. Such carbon acids are effective but easy-to-handle acid catalysts.
Summarized in this article are the syntheses of heterocyclic natural products by means of Rh-catalyzed C-H insertion reaction of diazoester. During the course of our total synthesis of (−)-ephedradine A (1) by application of Ns-strategy, we found that the Rh2(S-DOSP)4 mediated C-H insertion reaction was enabled to simplify the synthetic process and decided to use it for the natural product synthesis. In the synthesis of serotobenine (4), the C-H insertion precursor was efficiently synthesized by the Leimgruber-Batcho protocol and a regioselective Claisen rearrangement. The racemic nature of serotobenine (4) is suggested by the presence of p-quinonemethide intermediate 6. Enantioselective synthesis of SB-203207 (25a) was accomplished by desymmetric C-H insertion reaction of 33 for construction of a bicyclo[3.3.0] framework, stereoselective construction of sequential stereocenters of 37, novel conversion from an aldehyde to a carboxylic acid, and nitrile hydrolysis. Stereoselective synthesis of MFPA (54) was accomplished by intermolecular C-H insertion and the asymmetric center at the benzylic position of 58 permitted efficient incorporation of the three sequential stereochemistries on the pyrrolidine ring of 68. Synthesis of aperidine (70) was featured by the cis-selective construction of a dihydrobenzofuran ring of 82 utilizing by Hashimoto’s catalyst and preparation of diazoamide of 81 by Raines’ protocol.
Dearomatization reactions of phenols have been useful and powerful reactions for construction of highly substituted three-dimensional structures seen in natural products. Recently, several groups have achieved the intermolecular asymmetric dearomatization reactions by oxidative protocol. Toste’s group reported asymmetric non-oxidative dearomatization of phenol derivative under the phase-transfer catalysis. Very recently, You’s group reported metal-catalyzed asymmetric alkylation of naphthols with high enantioselectivity.
In this short review, reductive transformations of esters with SmI2-H2O system are described. Recently, reduction of esters into the corresponding alcohols and intramolecular cyclization of radical anions derived from single electron reduction of esters have been extensively studied as novel and efficient methods for organic syntheses. In these reactions, a single electron transfer from SmI2 to ester is a key step, which is promoted by addition of H2O.
Several enantioselective syntheses of axially chiral compounds have been recently accomplished by means of various organocatalysts. The strategies reported thus far can be classified into three manners including atroposelective formation of chiral axis, dynamic kinetic resolution, and desymmetrization. These organocatalytic methods opened new avenues for the construction of axial chirality, thereby leading to the synthesis of axially chiral compounds which have been synthetically challenging through conventional methods.