Selective Oxidation of Benzylic Alcohols and TBDMS Ethers to Carbonyl Compounds with CrO<sub>3</sub>-H<sub>5</sub>IO<sub>6</sub>
作者:Mark L. Trudell、Suhong Zhang、Liang Xu
DOI:10.1055/s-2005-869975
日期:——
Benzyl alcohols and benzyl TBDMS ethers were efficiently oxidized to the corresponding carbonylcompounds in high yield with periodic acid catalyzed by CrO 3 at low temperature (-78 °C). The oxidation procedure was highlyfunctional group tolerant and very selective for the TBDMS group over the TBDPS group.
<i>Z</i>-Selective Alkene Isomerization by High-Spin Cobalt(II) Complexes
作者:Chi Chen、Thomas R. Dugan、William W. Brennessel、Daniel J. Weix、Patrick L. Holland
DOI:10.1021/ja408238n
日期:2014.1.22
rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminateligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the
简单的末端烯烃异构化为具有 Z 立体化学的内部异构体的情况很少见,因为通常会形成更稳定的 E 异构体。我们在这里表明,由庞大的 β-二酮亚胺配体支撑的钴 (II) 催化剂具有适当的动力学选择性来催化一些简单的 1-烯烃的异构化,特别是作为稳定性较差的 Z-异构体的 2-烯烃。催化通过“烷基”机制进行,三配位钴 (II) 烷基配合物作为静止状态。如同位素标记实验所示,β-氢化物消除和 [1,2]-插入步骤都很快。立体模型通过在 β-氢化物消除的过渡态钴 (II) 处的方形平面几何结构来解释选择性。该催化剂不仅适用于简单的烯烃,还适用于高烯丙基硅烷、缩酮、和甲硅烷基醚。从与不良底物的反应中分离出钴 (I) 或钴 (II) 产物表明,关键的催化剂分解途径是双分子的,降低催化剂浓度通常会提高选择性。除了潜在有用的选择性转化之外,这些研究还为高自旋钴配合物催化烯烃异构化提供了机理理解,并证明了空间体
Zn-Mediated, Pd-Catalyzed Cross-Couplings in Water at Room Temperature <i>Without</i> Prior Formation of Organozinc Reagents
作者:Arkady Krasovskiy、Christophe Duplais、Bruce H. Lipshutz
DOI:10.1021/ja906803t
日期:2009.11.4
Mix in water, stir. That is all that is required in this new approach to sp(3)-sp(2) cross-couplings between an alkyl iodide and an aryl bromide, both potentially bearing functionality. They react under catalysis by Pd(0) in the presence of zinc powder, aided by a nonionic amphiphile, to give the alkylated aromatic. No organic solvents and no heating; just add water.
Novel Method for Efficient Aerobic Oxidation of Silyl Ethers to Carbonyl Compounds Catalyzed with <i>N</i>-Hydroxyphthalimide (NHPI) and Lipophilic Co(II) Complexes
作者:Babak Karimi、Jamshid Rajabi
DOI:10.1021/ol049294+
日期:2004.8.1
In this work, a new method for highly efficient and selective oxidative deprotection of a variety of structurally diverse trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) ethers using molecular oxygen in the presence of N-hydroxyphthalimide (NHPI) and various types of Co(II) complexes is reported. As a result of the relatively neutral reaction medium, acid-sensitive functional groups such as
A facile 1, 5-migration of tert-butyldimethylsilyl and tert-butyldiphenylsilyl groups in the Witting reaction and under other basic conditions was observed during synthetic studies on prostaglandins. A new method for the cleavage of these two silyl protecting groups to the parent alcohol was developed by the combined use of potassium superoxide and crown ether in dimethyl sulfoxide. Utilizing these new reactivities, an efficient synthesis of 11-epi-PGF2α from the well known Corey lactone was successfully achieved.