Horner-Wadsworth-Emmons Modification for Ramirez <i>gem-</i>Dibromoolefination of Aldehydes and Ketones Using P(O<i>i</i>-Pr)<sub>3</sub>
作者:Mark Lautens、Yuan-Qing Fang、Olga Lifchits
DOI:10.1055/s-2008-1032045
日期:2008.2
A simple procedure for the use of triisopropylphosphite in the Ramirez olefination is described. This reagent is equally or more reactive than PPh3 toward aldehydes and ketones in the gem-dibromoolefination of aldehydes and ketones. Under the reaction conditions, an α-bromoketone gave a novel tribromomethyl-substituted oxirane product in good yield. The substrate-dependent nature of this reaction suggests that this Horner-Wadsworth-Emmons equivalent of the Ramirez gem-dibromoolefination reaction proceeds through an ionic mechanism.
Benzocycloheptynedicobalt Complexes by Intramolecular Nicholas Reactions
作者:James R. Green、Yu Ding
DOI:10.1055/s-2004-837215
日期:——
Lewis acid mediated intramolecular Nicholas reactions of aryl (Z)-enyne propargyl acetate-Co2(CO)6 complexes 1 afford benzocycloheptenyne-Co2(CO)6 complexes 2 and their heterocyclic analogues.
Asymmetric hydrogenation is one of the most powerful methods for the preparation of single enantiomer compounds. However, the chemo- and enantioselective hydrogenation of the relatively inert unsaturated group in substrates possessing multiple unsaturated bonds remains a challenge. We herein report a protocol for the highly chemo- and enantioselective hydrogenation of conjugated enynes while keeping
不对称氢化是制备单一对映体化合物的最有效方法之一。然而,在具有多个不饱和键的底物中相对惰性的不饱和基团的化学和对映选择性氢化仍然是一个挑战。我们在此报告了共轭烯炔的高度化学和对映选择性氢化同时保持炔键完整的协议。机理研究表明,Co II 配合物的锌还原产生的伴随的 Zn 2+在启动合理的 Co I /Co III催化循环中起着关键作用。这种方法可以高效生成手性炔丙胺(高达 99.9 % ee 和 2000 S/C)和进一步有用的化学转化。
Practical Synthesis of (<i>Z</i>)-Polyaromatic and Heteroaromatic Vinylacetylenes
[reaction: seet text] Two synthetic routes to several (Z)-polyaromatic and heteroaromatic substituted vinylacetylenes are described. The nature of aryl- or heteroaryl-substituted carboxaldehyde used as starting material dictated the choice of Wittig salt employed. A very attractive way to construct polyaromatic and pyridine-containing enynes is the reaction of polyaromatic and pyridine-containing aldehydes