Nakcheol Jeong

Asymmetric catalytic reactions by NbO-type chiral metal–organic frameworks

Chiral metal–organic frameworks (MOFs) constitute a unique class of multifunctional hybrid materials and are envisioned as a versatile tool for various enantioselective applications, including the separation of optical isomers and the promotion of catalytic enantioselective reactions. Despite some pioneering works on catalytic enantioselective reactions promoted by chiral MOFs, there is still a need for practical catalysts and many fundamental issues must be answered; such as pin-pointing the site of the reaction and expedition of the reaction rate to the level of that in homogeneous media. We have designed and synthesized a chiral metal–organic framework, (S)-KUMOF-1 (Cu2(S)-1)2(H2O)2, 1 = 2,2′-dihydroxy-6,6′-dimethyl(1,1′-biphenyl)-4,4′-dicarboxylate) of which a non-interpenetrating NbO type framework provides a spacious pore (2 × 2 × 2 nm3) and is equipped with potential catalytic sites exposed into the pore. Since the functional group on the organic links, biphenols in this MOF, can be modified further on demand, this MOF can serve as a platform for new heterogeneous catalysis. Two reactions, the carbonyl-ene reaction with modified MOF after replacement of the protons on biphenol on the organic links with Zn(II) and the hetero-Diels–Alder reaction with Ti(IV), respectively, were studied. In this manoeuver, we observed that the reaction occurs entirely inside the pores and the reaction rate of the heterogeneous reaction by this specific MOF is comparable to that of its homogeneous counterpart. In addition, it is also observed that the enantioselectivities are significantly improved by extra steric bias provided from the frames of the MOF. These observations reinforce the legitimacy of the strategy of using a chiral MOF as a highly enantioselective heterogeneous catalyst.

Pauson­Khand-type reaction mediated by Rh(I) catalysts

Cocyclization of alkynes, alkenes, and carbon monoxide by transition metals (known as PausonKhand reaction when dicobalt octacarbonyl complexes are used) has been accepted as one of the most powerful tools in the synthesis of cyclopentenones. Despite significant progress in the various aspects of the reaction, we still needed new catalysts to expand the scope of the reaction further. We found rhodium (I) catalysts, e.g., RhCl(PPh3)3, trans-RhCl(CO)(PPh3)2, RhCl-(CO)(dppe), and trans-[RhCl(CO)(dppp)]2, were also effective for this transformation. The scope and the efficiencies of the reaction could be tuned and expanded by the choice of catalysts. For example, we were able to devise an enantioselective PK-type reaction and a tandem strategy employing two catalysts in one pot. These results will be presented.

Asymmetric Pauson−Khand-type Reaction Mediated by Rh(I) Catalyst at Ambient Temperature

An efficient asymmetric PKR mediated by Rh(I) catalyst at ambient temperature was developed. The reaction utilizing a Rh(I) catalyst bearing a (R)-3,5-diMeC4H4-BINAP ligand at 18-20 degrees C under a reduced partial pressure of CO (0.1 atm) provided PKR products in high chemical yield as well as high enantioselectivity.

Catalytic Intermolecular Pauson – Khand Reactions in Supercritical Ethylene

Ethylene is not only a substrate, but also a solvent: Catalytic intermolecular Pauson - Khand reactions of terminal alkynes were carried out in supercritical ethylene to provide 2-substituted cyclopentenones in moderate to high yields [Eq. (1)]. Under these conditions, even a low pressure of CO (5 atm) is sufficient for the reaction to take place.

Linkage of N3 dye to N3 dye on nanocrystalline TiO2 through trans-1,2-bis(4-pyridyl)ethylene for enhancement of photocurrent of dye-sensitized solar cells

Linking of N3 dye to another TiO2-attached N3 dye rendered an enhanced short-circuit photocurrent and thereby higher efficiency for the dye-sensitized solar cell with the pertinent TiO2 film electrode.

Internal chelation-guided regio- and stereoselective Pauson-Khand-type reaction by chiral rhodium(I) catalysis.

Internal chelation-assisted transition-metal-catalyzed reactions have attracted considerable interest and can often provide new opportunities for previously formidable reactions. For example, C C bond activation followed by cleavage and hydroacylation for the preparation of mediumsized (larger than five-membered) heteroatom-containing (O, S, N) rings, have been realized using internally chelated rhodium(I) catalysts. Rhodium(I) catalysts might have potential chelation effects in the asymmetric Pauson–Khand reaction (APKR) but the internal chelation-assisted rhodium(I)-catalyzed PKR has not yet been addressed. Herein, we report the chelation-guided regioand stereoselective Pauson–Khandtype reaction by rhodium(I) catalysts. A review of previous studies of rhodium(I)-catalyzed APKR (Scheme 1) revealed a couple of unique features that suggest the intervention role of oxygen atoms in the reaction. First, the APKR by the cationic rhodium(I) catalyst was much faster and provided significantly higher enantioselectivity in tetrahydrofuran than in toluene. The rationale behind this is as follows. Portions of the proposed catalytic species, which are in a dynamic equilibrium, are changeable depending on the solvent (Scheme 2). A significant amount of the catalytic species 3, which is more reactive than 4 and

A chiral trianglular coordination complex derived from (S,S)-1,2-dimethoxy-di-4-(2′-carboxyl-5′-pyridyl)phenyl ethane and Cu(II) by self-assembly

A chiral triangular coordination complex 6 has been obtained through the self-assembly of three copper(II) ions and three chiral organic dicarboxylate ligand ((S,S)-5H2) having C2 symmetry.

Pauson–Khand Reaction

This chapter updates the recent advances in the study of the well-known synthetic method for organometallic compounds, namely, the Pauson–Khand reaction (PKR). The principal emphasis is on the progress since 1993. Developments and variations in stoichiometric PKRs are first addressed. Advances in catalytic versions, including heterogeneous as well as the enantioselective ones, and related cycloadditions are covered next. Finally, the applications of the PKRs are highlighted.

Desymmetrization of meso-dienyne by asymmetric Pauson?Khand type reaction catalystsElectronic supplementary information (ESI) available: experimental section. See http://www.rsc.org/suppdata/cc/b4/b401288g/

Desymmetrization of the meso dienynes, such as propargyl 1-vinylallyl N-tosylamides (1a-c) and propargyl 1-vinylallyl ethers (1d-e), by asymmetric Pauson-Khand type reaction catalysts was studied. The corresponding vinyl substituted bicyclic pentenones (2 and 3) were obtained with high diastereoselectivity and enantioselectivity.

The 2-(4-trifluoromethylphenylsulfonyl)ethoxycarbonyl (Tsc) amino-protecting group: use in the solid-phase synthesis of pyrrole-imidazole polyamides

The development of the 2-(4-trifluoromethylphenylsulfonyl)ethoxycarbonyl (Tsc) function, a novel base-sensitive amino-protecting group, and its application to the preparation of DNA-binding polyamides are described. Pyrrole–imidazole polyamides were synthesized by an efficient solid-phase method under conditions compatible with Fmoc chemistry using two Tsc-protected amino acids, Tsc-Py-OH 1a and Tsc-Im-OH 1b.