OH Bond Activation Research Articles

Direct sulfanylation of 4-hydroxycoumarins with thiols in water

The direct sulfanylation of 4-hydroxycoumarins with thiols via C–OH bond activation in water under mild conditions is described, which afforded the corresponding 4-sulfanylcoumarins in good yields.

Palladium-catalyzed direct arylation of 4-hydroxycoumarins with arylboronic acids via C–OH bond activation

Operationally simple PdCl 2-catalyzed direct arylation of 4-hydroxycoumarins with arylboronic acids via C–OH bond activation under mild conditions is described, which gave rise to the corresponding 4-arylcouamrins in good to excellent yields.

Phosphonium Coupling in the Direct Bond Formations of Tautomerizable Heterocycles via C–OH Bond Activation

AbstractSince the original report in 2004, phosphonium coupling has emerged as a new, mild, efficient, chemoselective and versatile methodology for the direct C–C, C–N, C–O, and C–S bond formations of unactivated and unprotected tautomerizable heterocycles. Phosphonium coupling proceeds via C–OH bond activation of a tautomerizable heterocycle with a phosphonium salt (e.g., PyBroP), and subsequent functionalization with either a nucleophile through SNAr displacement or an organometallic through transition‐metal‐catalyzed cross‐coupling. As the first direct bond formation via C–OH bond activation, phosphonium coupling offers a powerful and practical methodology that features operational simplicity, functionality compatibility, and broad substrate scope. Its attractive protecting‐group‐free direct bond formation involving a domino multiple‐step process in a single step provides unique and facile access to many biologically important heterocycles including macromolecules with sensitive functionalities (e.g., DNA, RNA and PNA building blocks). Consequently, the discovery of phosphonium coupling has finally enabled a single‐step transformation in nucleoside chemistry, which has been an unsolved synthetic challenge in the past half‐century. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Phosphonium Coupling in the Direct Bond Formations of Tautomerizable Heterocycles via C–OH Bond Activation (Eur. J. Org. Chem. 4/2009)

AbstractThe cover picture shows the single‐step direct transformations of inosine into C6‐functionalized nucleosides by base‐promoted or palladium‐catalyzed phosphonium couplings. Since the pioneering work by Fox et al. in 1958, the functionalization of nucleosides has been routinely carried out in a multi‐step sequence including protection, activation, functionalization, and deprotection. As the first direct bond formation through C–OH bond activation of tautomerizable heterocycles with PyBroP, this new, mild, efficient, chemoselective, and versatile phosphonium coupling methodology has solved a long‐standing synthetic challenge of a single‐step transformation in nucleoside chemistry. Details of the discovery, mechanism, scope, and application of this technology are presented in the Microreview by F.‐A. Kang et al. on p. 461 ff.

Graphical Abstract: Eur. J. Org. Chem. 4/2009

AbstractThe cover picture shows the single‐step direct transformations of inosine into C6‐functionalized nucleosides by base‐promoted or palladium‐catalyzed phosphonium couplings. Since the pioneering work by Fox et al. in 1958, the functionalization of nucleosides has been routinely carried out in a multi‐step sequence including protection, activation, functionalization, and deprotection. As the first direct bond formation through C–OH bond activation of tautomerizable heterocycles with PyBroP, this new, mild, efficient, chemoselective, and versatile phosphonium coupling methodology has solved a long‐standing synthetic challenge of a single‐step transformation in nucleoside chemistry. Details of the discovery, mechanism, scope, and application of this technology are presented in the Microreview by F.‐A. Kang et al. on p. 461 ff.

Competitive O–H and C–H oxidative addition of CH3OH to rhodium(ii) porphyrins

Rhodium(II) porphyrins react with CH(3)OH in benzene by alternate mechanisms that give H-CH(2)OH and H-OCH(3) bond activation in different methanol concentration regimes which is a rare example of transition metal reactivity with methanol.

TiO2(110) 표면에 흡착된 물분자의 결합 활성화에 관한 MO 연구

<TEX>$TiO_2$</TEX>(110) 표면에서 물의 OH 결합 활성화가 어떤지 전자적 메카니즘에 의해 이루어지는 extended Hiickel 방법을 통해 알아보았다. 물분자는 <TEX>$3a_1$</TEX>오비탈의 시그마 상호작용 겨로가로 5배위 <TEX>$Ti^{4+}$</TEX>원자바로위에 수직으로 흡착한다. 이 결합구조에서는 물분자의 H원자가 <TEX>$TiO_2$</TEX>의 2배위 bridging <TEX>$O^{2-}(O_b)$</TEX>원자와 너무 멀리 떨어져 있으므로 OH 결합 해리를 촉진시키는 수소결합 상호 작용을 할 수 없으므로 물분자를 <TEX>$O_b$</TEX> 원자쪽으로 기울여 수소결합이 형성되도록 한다. 이 경우 <TEX>$O_b$</TEX> P 오비탈로부터 흡착 물분자의 LUMO <TEX>$2b_1$</TEX>반 결합성 오비탈로 전자밀도의 이동이 일어나고 또 물의 <TEX>$3a_1$</TEX>오비탈(약한 결합성)로부터 <TEX>$Ti^{4+} 3d_{z2}$</TEX>오비탈로 전자밀도의 이동이 일어남으로써 물의 OH 결합이 상당히 약화됨을 확인할 수 있었고 그 결과 OH와 H로 해리할 것이라는 해석이 가능하다. A molecular orbital analysis based on the extended Huckel calculations has been carried out to study the OH bond activation of water on the <TEX>$TiO_2$</TEX>(110) surface. <TEX>$H_2O$</TEX> binds with its axis perpendicular to the surfac on top of the five-coordinate <TEX>$Ti^{4+}$</TEX> atom via its <TEX>$3a_1$</TEX> orbital. In this bonding situation, the two-coordinated bridging <TEX>$O^{2-}$</TEX> atom (<TEX>$O_b$</TEX>, basic site) on <TEX>$TiO_2$</TEX>(110) is too distant from an H atom of water to form hydrogen-bondig interactions with water that facilitate O-H bond cleavage. It has been elucidated that the O-H bond is appreciably weakened when the water molecule is tilted to give a hydrogen bond with the <TEX>$O_b$</TEX> atom. This mechanism includes mutual transfer of electron density from the <TEX>$3a_1$</TEX> orbital of the water molecule to the <TEX>$Ti^{4+} 3d_{z2}$</TEX> orbital and from the <TEX>$O_b$</TEX> P orbitals to the <TEX>$2b_1$</TEX> of the adsorbed water molecule This should result in lengthening of the O-H bond in the surface complex and the subsequent dissociation into the fragments OH and H.