Asymmetric Total Synthesis of (−)-Amphidinolide V through Effective Combinations of Catalytic Transformations
作者:Ivan Volchkov、Daesung Lee
DOI:10.1021/ja401717b
日期:2013.4.10
The synthesis features a base-catalyzed alkynyl silane alcoholysis/ring-closing enyne metathesis sequence for facile construction of a 1,3-diene motif. A diene RCM followed by a ring-contractive allylic transposition of cyclic silyl ethers was incorporated for the stereoselective installation of a functionalized 1,5-diene subunit. An efficient proline-mediated direct cross-aldol condensation of two
完成了 (-)-amphidinolide V 的不对称全合成。该合成具有碱催化的炔基硅烷醇解/闭环烯炔复分解序列,可轻松构建 1,3-二烯基序。引入二烯 RCM,然后是环状甲硅烷基醚的缩环烯丙基转座,用于立体选择性安装功能化的 1,5-二烯亚单元。两种高级醛中间体的高效脯氨酸介导的直接交叉羟醛缩合被用于构建关键的 α,β-不饱和环氧醛。这种全合成证明了金属催化转化在复杂分子合成中的威力。
Chiral Silylation Reagents for the Determination of Absolute Configuration by NMR Spectroscopy
作者:Douglas B. Weibel、Tameka R. Walker、Frank C. Schroeder、Jerrold Meinwald
DOI:10.1021/ol006162h
日期:2000.7.1
We have investigated the use of chiral silylating reagents as analytical probes for determining the absolutestereochemistry of naturalproducts by NMR spectroscopy. These reagents are prepared in high chemical yield in one step and can be used to derivatize chiralallylic alcohols which are incompatible with ester-based methodologies. Microscale ( approximately 400 nmol) derivatization conditions
alpha-positions of thiophenes. Asymmetric synthesis is carried out using (-)-sparteine-mediated annelation of the axially chiral bis(aryllithium) with electrophilic sulfur equivalent. Alternatively, enantiomers of the [7]helicene are obtained via resolution using menthol-based chiral siloxanes. Racemic [7]helicene and four other macrocyclic products of the annelation are characterized by X-ray crystallography
描述了一种新型低聚噻吩的合成和表征,其中噻吩环退火成具有交叉共轭 pi 系统的 [7] 螺旋。这种 [7] 螺旋可以被视为前所未有的碳硫 (C(2)S)(n)() 螺旋的碎片,拥有富含硫的分子外围。[7] helicene 的外消旋合成基于两个步骤的迭代交替:噻吩的 β 位之间的 CC 键同源偶联和噻吩的 α 位之间的退火。使用 (-)-sparteine 介导的轴向手性双(芳基锂)与亲电子硫等价物的退火进行不对称合成。或者,[7]螺旋烯的对映异构体通过使用基于薄荷醇的手性硅氧烷拆分获得。外消旋 [7] helicene 和退火的其他四种大环产物通过 X 射线晶体学表征。[7] helicene 的一种溶剂多晶型物具有相反对映异构体的 pi 堆积柱和多个短分子间接触,包括同手性和异手性短 S...S 接触,表明在二维中存在有效的分子间电子耦合。[7]螺旋烯在室温下构型稳定,在 199 摄氏度时外消旋,半衰期约为
GENERATION OF NONRACEMIC 2-(t-BUTYLDIMETHYLSILYLOXY)-3-BUTYNYLLITHIUM FROM (S)-ETHYL LACTATE:
作者:Marshall, James A.、Yanik, Mathew M.、Adams, Nicholas D.、Ellis, Keith C.、Chobanian, Harry R.、Gudipati, Venugopal、Turner, Tiffany、Curran, Dennis P.
DOI:10.15227/orgsyn.081.0157
日期:——
Functionalized Thiophene-Based [7]Helicene: Chirooptical Properties versus Electron Delocalization
The functionalized, enantiomerically pure [7]helicene 1 derived from bis(benzodithiophene) functionalized with four heptyl groups is prepared from 1,8-dibromo-4,5-diheptylbenzo[1,2-b:4,3-b']dithiophene building block 2. Such [7]helicene structure, functionalized with bromines at the terminal positions of the helicene inner rim and multiple solubilizing alkyl groups, is an attractive building block for long [n]helicenes and oligo[7]helicenes. Chirooptical properties and the degree of electron delocalization are determined and compared to those of analogous carbon-sulfur [7]helicene and [7]helicenes derived from benzodithiophene to provide a correlation between chirooptical properties and the degree of electron delocalization. [7]Helicene 1 possesses a moderately increased electron delocalization, but its chirooptical properties are similar to those for analogous [7]helicenes with relatively lower electron delocalization, indicating that chirooptical properties are not significantly affected by electron delocalization for this series of [7]helicenes. Molecular structures of racemic [7]helicene 1 and its benzodithiophene building block 2 are confirmed by single-crystal X-ray analysis. Crystals of 2 are chiral and adopt the shape of long, flexible, flat needles that can be readily bent.