Amides as precursors of imidoyl radicals in cyclisation reactions
作者:W. Russell Bowman、Anthony J. Fletcher、Jan M. Pedersen、Peter J. Lovell、Mark R.J. Elsegood、Elena Hernández López、Vickie McKee、Graeme B.S. Potts
DOI:10.1016/j.tet.2006.10.030
日期:2007.1
Amides have been successfully used as precursors of imidoyl radicals for radical cyclisation. The amides have been converted to imidoyl selanides via reaction with phosgene to yield imidoyl chlorides followed by reaction with potassium phenylselanide. Imidoyl selanides were reacted with tributyltin hydride (Bu3SnH) as the radical mediator with triethylborane or AIBN as initiators to yield imidoyl radicals
Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 6. Pyrolysis of substituted cinnamoyl ylides as a route to conjugated enynes
作者:R. Alan Aitken、Christine Boeters、John J. Morrison
DOI:10.1039/p19940002473
日期:——
The substituted cinnamoyl ylides 6 and 7, readily prepared in one step from the quaternary phosphonium salts 8 and cinnamoyl chlorides 9, undergo extrusion of Ph3PO upon FVP to give the 1,3-enynes 12 and 13 in moderate yield. At 500 °C there is little double bond isomerisation, but at 700 °C this does occur to give almost 1:1 mixtures of E and Z isomers. In a few cases, including those with a nitrophenyl
由季phospho盐8和肉桂酰氯9一步制备的取代肉桂酸酯基化物6和7在FVP上经过Ph 3 PO挤出,以中等收率得到1,3-烯炔12和13。在500°C下几乎没有双键异构化,但是在700°C时确实发生了几乎1:1的E和Z混合物异构体。在少数情况下,包括存在硝基苯基的情况,收率很低或反应完全失败。通过使用酯稳定的内酯来改善1-苯基丁烯的不良产率的尝试仅部分成功,因为失去酯基所需的苛刻条件导致明显的异构化为萘。报告了20个炔的完全归属的13 C NMR光谱。已经制备了一个异构体β,γ-不饱和-δ-氧代酰化物的例子,14,发现在700°C下FVP上的Ph 3 P损失,从而以低收率得到了茚和苯。
Phosphinalkylene, 51<sup>1</sup>; Synthese und Reaktionen von [1-(Trialkylsilyl)alkyliden]triphenylphosphoranen
作者:Hans Jürgen Bestmann、Andreas Bomhard、Roman Dostalek、Rainer Pichl、Roland Riemer、Reiner Zimmermann
DOI:10.1055/s-1992-26227
日期:——
Synthesis and Reactions of [1-(Trialkylsilyl)alkylidene[triphenylphosphoranes Alkylidenetriphenylphosphoranes 1 react with trialkyl halosilanes 2 to afford silylated alkylidenephosphoranes 5, which can be converted to acylated alkylidenephosphoranes 8 and 10 by trimethylsilyl carboxylates 6 or carboxylic anhydrides 10. Bis(acylalkylidenephosphoranes) 13-15 are available from 5 and bis(trimethylsilyl) dicarboxylates 12 or cyclic or polymeric anhydrides 16, 17.
Treasures from the Free Radical Renaissance Period – Miscellaneous hexenyl radical kinetic data
作者:Athelstan L. J. Beckwith、Carl H. Schiesser
DOI:10.1039/c0ob00708k
日期:——
Rate constant data and Arrhenius parameters have been determined for a series of substituted hexenyl radicals of differing electronic and steric demand. Electron-withdrawing groups (CF3, CO2Et) directly attached to the radical centre slighly accelerate 5-exo ring-closure (kcis + ktrans ∼ 2.1 × 105 s−1 at 25°) relative to donating groups (OMe; 1.6 × 105 s−1 at 25°). Sterically demanding groups (tert-Bu)
已针对一系列具有不同电子和空间需求的取代己烯基确定了速率常数数据和Arrhenius参数。相对于捐赠基团(OMe ),直接连接至自由基中心的吸电子基团(CF 3,CO 2 Et)缓慢促进5- exo闭环(25°时k cis + k trans〜2.1 ×10 5 s -1) ;在25°时为1.6×10 5 s -1)。如预期的那样,对空间要求较高的组(叔-Bu )减慢环化过程(1×10 5 s -1)。这些观察结果与5 - exo闭环的活化能的细微变化是一致的。有趣的是,溶剂的性质似乎对该化学有重大影响,随着溶剂极性的增加,顺式/反式立体选择性有时会提高。除了包含CF 3(吸电子)基团的系统显示出环化/捕获速率常数(k c / k H)增加外,k c / k H普遍下降。记录随着溶剂极性增加的比率;据推测,这些变化主要是由于所用各种溶剂中k H的变化引起的。
Novel<i>ortho</i>-Alkoxy-Substituted Phosphorus Ylides and Their Stereoselectivity in Witting Reactions
The stereochemistry of the reactions between tris(2-methoxy-methoxyphenyl)phosphonioethanide (1f), -butanide (2f), and -phenyl-methanide (3f) and a variety of aldehydes was investigated. Ylides having a β-unbranched aliphatic sidechain, such as 2f, and saturated straight-chain aldehydes give olefins with unprecedented cis-selectivity (cis/trans â 200:1).