Dihydroquinidine acetate promoted osmylation of acetals of E-α,β- unsaturated aldehydes occurs with up to 40:1 stereoselection to afford the corresponding protected -α,β -dihydroxy aldehydes.
An ingenious method for the determination of the relative and absolute configurations of compounds containing aryl-glycerol fragments by <sup>1</sup>H NMR spectroscopy
established to determine the relative and absolute configurations of aryl-glycerols that depend on the chemical shift differences (Δδ) of the diastereotopic methylene protons (H-3) by 1HNMRspectroscopy. When using DMSO-d6 as the preferred solvent, the threo configuration corresponded to a larger ΔδH3a–H3b value (>0.15 ppm), whereas the erythro configuration (<0.07 ppm) corresponded to a smaller value
建立了一种简明的方法来确定芳基甘油的相对和绝对构型,该构型取决于非对映亚甲基质子(H-3)的化学位移差异( Δδ ),通过1 H NMR 光谱。当使用 DMSO- d 6作为首选溶剂时,苏型构型对应于较大的 Δ δ H3a–H3b值 (>0.15 ppm),而赤型构型 (<0.07 ppm) 对应于较小的值。此外,借助莰酰氯的简单酰化反应确定了绝对构型。在苏式对映体中, 1R , 2R构型的Δδ值为<0.15ppm, 1S , 2S构型的Δδ值为>0.20ppm。赤型对映体中,1 R ,2 S的Δδ值为>0.09 ppm,1 S ,2 R的Δδ值为<0.05 ppm。值得注意的是,这个经验规则在CDCl 3中是无效的。此外,该方法还通过量子1 H NMR计算得到验证。
The <sup>1</sup>H NMR Method for the Determination of the Absolute Configuration of 1,2,3-<i>p</i><i>rim</i>,<i>s</i><i>ec</i>,<i>s</i><i>ec-</i>Triols
作者:Enrique Lallana、Félix Freire、José Manuel Seco、Emilio Quiñoá、Ricardo Riguera
DOI:10.1021/ol0616135
日期:2006.9.1
comparison of the 1HNMR spectra of the tris-(R)- and the tris-(S)-MPA ester derivatives. An experimental demonstration of this correlation with 24 triols of known absolute configuration and a protocol using two parameters-Deltadelta(RS)(H3) and the difference between Deltadelta RS (H2) and Deltadelta RS (H3) = absolute value (Delta(Deltadelta RS))-for its application to the determination of the absolute
Conversion of oxiranes and CO2 to organic cyclic carbonates using a recyclable, bifunctional polystyrene-supported organocatalyst
作者:Christopher J. Whiteoak、Andrea H. Henseler、Carles Ayats、Arjan W. Kleij、Miquel A. Pericàs
DOI:10.1039/c3gc41919c
日期:——
The development of a heterogeneous one-component bifunctional catalyst system able to catalyse the conversion of carbon dioxide and oxiranes to organic cyclic carbonates at low temperature (45 °C) is reported. The bifunctional system can be easily recycled and reactivated when required. When compared with other heterogeneous organocatalysts for the same transformation, the reported catalyst is active at much milder temperatures, thus emphasising the optimal sustainability profile of the new catalyst system.
stereocomplementary D‐fructose‐6‐phosphate aldolase and L‐rhamnulose‐1‐phosphate aldolase is performed. Both aldolases accept unphosphorylated donor substrates, avoiding the need of handling the phosphate group that the dihydroxyacetone phosphate‐dependent aldolases require. In this way, 6‐C‐aryl‐L‐sorbose, 6‐C‐aryl–L‐fructose, 6‐C‐aryl–L‐tagatose, and 5‐C‐aryl‐L‐xylose derivatives are prepared by using this