Regioselectivity Influences in Platinum-Catalyzed Intramolecular Alkyne O–H and N–H Additions
作者:Jeff P. Costello、Eric M. Ferreira
DOI:10.1021/acs.orglett.9b03557
日期:2019.12.20
The steric and electronic drivers of regioselectivity in platinum-catalyzed intramolecular hydroalkoxylation are elucidated. A branch point is found that divides the process between 5-exo and 6-endo selective processes, and enol ethers can be accessed in good yields for both oxygen heterocycles. The main influence arises from an electronic effect, where the alkyne substituent induces a polarization
s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols
作者:Michael Fairley、Laia Davin、Alberto Hernán-Gómez、Joaquín García-Álvarez、Charles T. O'Hara、Eva Hevia
DOI:10.1039/c9sc01598a
日期:——
robustness of 18-crown-6/K2MgR4(PMDETA)2 as a catalyst. A wide series of alkynols, including terminal and internalalkynes which contain a variety of potentially reactive functional groups, were cyclised. In comparison to previously reported monometallic systems, bimetallic 18-crown-6/K2MgR4(PMDETA)2 displays enhanced reactivity towards internal alkynol-cyclisation. Kinetic studies revealed an inhibition
混合 s-嵌段金属有机金属试剂已成功用于炔醇的催化分子内加氢烷氧基化。这一成功归因于这些试剂可以克服反应挑战的独特方式:即 OH 活化和配位,然后通过 C C 键加成。为了优化反应条件并满足重要的催化体系要求,一系列碱金属镁酸盐被用于催化 4-戊炔醇的分子内加氢烷氧基化。在主要研究的前奏中,同金属二烷基镁试剂 MgR 2(其中 R = CH 2 SiMe 3) 被使用。即使在多齿路易斯供体分子如N、N、N '、N ''、N ''的存在下,该试剂也不能成功地将醇环化为 2-亚甲基四氢呋喃2a或 5-甲基-2,3-二氢呋喃2b -五甲基二亚乙基三胺 (PMDETA)。碱金属镁酸盐 M I MgR 3 (当 M I = Li、Na 或 K) 在N、N、N '、N'-四甲基乙二胺 (TMEDA) 或 PMDETA不存在/存在下均不能令人满意地进行环化。当高阶镁化(即,使用 M I 2 MgR 4 ),通常观察到
Alkaline Earth Catalysis of Alkynyl Alcohol Hydroalkoxylation/Cyclization
作者:Christine Brinkmann、Anthony G. M. Barrett、Michael S. Hill、Panayiotis A. Procopiou、Stephanie Reid
DOI:10.1021/om3008663
日期:2012.10.22
Heavier alkaline earth bis(trimethylsilyl)amides [AeN(SiMe3)(2)}(2)](2) (Ae = Ca, Sr, Ba) are shown to act as effective precatalysts for the regioselective intramolecular hydroalkoxylation/cyclization of a wide range of alkynyl and allenyl alcohols. In the majority of cases, cyclization of alkynyl alcohols produces mixtures of the possible endo- and exocyclic enol ether products, rationalized as a consequence of alkynylalkoxide isomerization to the corresponding allene derivatives. Cyclization rates for terminal alkynyl alcohols were found to be significantly higher than for substrates bearing internal alkynyl substituents, while the efficacy of cyclization was in general found to be determined by a combination of stereoelectronic influences and the thermochemical viability of the specific alkaline earth metal catalysis, which we suggest is determined by the individual M-O bond strengths. Kinetic studies have provided a rate law pertaining to a pronounced catalyst inhibition with increasing [substrate], indicating that turnover-limiting insertion of C-C unsaturation into the M-O bond requires the dissociation of substrate molecules away from the Lewis acidic alkaline earth center.
The preparation of (α-alkylidene)tetrahydrofurans by tungsten catalyzed decarboxylation of aldol precursors
作者:Tomoya Tanzawa、Jeffrey Schwartz
DOI:10.1016/s0040-4039(00)61775-6
日期:1992.11
A series of substituted (alpha-alkylidene)tetrahydrofurans was prepared by tungsten catalyzed reaction of substituted hydroxyfuroic acids. These reactions likely involve beta-lactone intermediates which decarboxylate under the reaction conditions, and rates for olefin synthesis correlated with donor properties of substituents at C(4).
Synthesis of functionalized THF and THP through Au-catalyzed cyclization of acetylenic alcohols
作者:Hassina Harkat、Jean-Marc Weibel、Patrick Pale
DOI:10.1016/j.tetlet.2006.12.100
日期:2007.2
omega-Acetylenic alcohols are regio- and stereo-selectively converted to the corresponding alpha-alkylidene oxygenated heterocycles in the presence of catalytic amounts of AuCl and K2CO3. (c) 2007 Elsevier Ltd. All rights reserved.