作者:Stephen R Davies、Michael C. Mitchell、Christopher P Cain、Paul G Devitt、Roger J Taylor、Terence P Kee
DOI:10.1016/s0022-328x(97)00176-9
日期:1998.1
9×10−2 mol−1 dm3 h−1, 293 K). However, one of the major limitations of this model is that competitive product inhibition dominates after some 15 turnovers (75% completion). Model studies reveal that hydrophosphonylation catalysis via a nitrogen Lewis base is accelerated up to 10-fold upon the introduction of [Zn(OSO2CF3)2] as co-catalyst. Consequently, Class II.1 systems employ metal salts [Zn(OSO2CF3)2]
我们在这里报告了一种精确的原位31 P 1 H} -NMR方法,用于测定α-羟基膦酸酯(羰基羰基膦酰化反应(Pudovik)反应的产物)的对映体纯度。该方法基于二氮杂膦烷手性衍生剂(CDA),该试剂满足精确测定的所有标准;(i)α-羟基膦酸酯的衍生既快速又干净,(ii)缺乏动力学拆分,并且(iii)31 P 1 H}化学位移分散体非常出色(> 5ppm)。通过交叉引用从CDA衍生的(MeO)2的酯获得的31 P 1 H} -NMR信号,实现了该测定的校准从脂肪酶催化的(MeO)2 P(= O)CHPh(OAc)水解(F-AP 15,米根霉(Rhizopuus oryzae))获得的鳞状物质中,用P(= O)CHPh(OH)进行旋光度测量。对一系列密切相关的衍生化α-羟基膦酸酯的NMR化学位移和偶合参数的分析在推断的基础上支持进一步的构型分配。我们还报告了在酸,有机氮碱和金属盐存在下α-羟基膦酸酯的构型稳定性。2
β-Amino alcohols derived from (1R,2S)-norephedrine and (1S,2S)-pseudonorephedrine as catalysts in the asymmetric addition of diethylzinc to aldehydes
作者:Raleigh W. Parrott、Shawn R. Hitchcock
DOI:10.1016/j.tetasy.2007.11.027
日期:2008.1
A family of N-alkylnorephedrine and N-alkylpseudonorephedrine derived ligands were prepared and applied in the asymmetric alkylation of benzaldehyde using diethylzinc. The absolute configuration of the addition product was directed primarily by the benzylic position of the Ephedra alkaloid, while the magnitude of the enantiomeric ratio was heavily influenced by the nitrogen substituent. However, sterically demanding substituents at the nitrogen position caused the enantioselectivity to be the same for the two diastereomeric systems. Among the ligands that were prepared, it was determined that the N-cyclooctylpseudonorephedrine derivative 7b yielded the highest enantiomeric ratios (87.5:12.5 to 91.0:9.0) when applied in the catalytic asymmetric addition of diethylzinc to aldehydes. (c) 2007 Elsevier Ltd. All rights reserved.
N-Pyridylmethylephedrine derivatives in the catalytic asymmetric addition of diethylzinc to aldehydes and diphenylphosphinoylimines
作者:Sucharita Banerjee、Jonathan A. Groeper、Jean M. Standard、Shawn R. Hitchcock
DOI:10.1016/j.tetasy.2009.08.014
日期:2009.9
N-Pyridylmethyl-substituted Ephedra derivatives were synthesized by either direct alkylation or reductive alkylation of (1R,2S)-norephedrine, (1S,2S)-pseudo norephedrine, and (1R,2S)-ephedrine. These derivatives were then employed in asymmetric addition reactions with diethylzinc and aldehydes and diphenylphosphinoylimines. The use of the diastereomers from the Ephedra family allowed for a systematic evaluation of the contribution of the N-pyridylmethyl. (C) 2009 Elsevier Ltd. All rights reserved.
Stereoselective synthesis of β-lactams by condensation of titanium enolates of 2-pyridyl thioesters with imines bearing a chiral auxiliary
tested as chiral auxiliaries in the stereoselectivesynthesis of β-lactams by condensation of the titanium enolates of 2-pyridyl thioesters with chiral imines. The amines were selected among the following classes of compounds: benzylic amines, β-aminoalcohols, β-heterosubstituted α-aminoesters. Inexpensive and available in both enantiomeric forms α-methylbenzylamine was identified as the chiral auxiliary
The Use of Benzamide Derivatives of Secondary Amines for Stereochemical Studies by Circular Dichroism
作者:Jacek Gawroński、Halina Kołbon、Marcin Kwit
DOI:10.1080/10242430212196
日期:2002.3
The benzamide chromophore is widely used as a Cottonogenic derivative of primary amines for stereochemical studies by circular dichroism. The assignments based on the exciton chirality method are reliable since the benzamide group has well-defined geometry and conformation. A recent report (J.D. Chisholm, J. Golik, B. Krishnan, J.A. Matson, D.L. Van Vranken, J. Am. Chem. Soc. 1999, 121: 3801-3802)
苯甲酰胺发色团广泛用作伯胺的产棉衍生物,用于通过圆二色性进行立体化学研究。由于苯甲酰胺基团具有明确定义的几何构型,因此基于激子手性方法的分配是可靠的。最近的一份报告(JD Chisholm,J。Golik,B。Krishnan,JA Matson,DL Van Vranken,J。Am。Chem。Soc。1999,121:3801-3802)要求将激子手性方法应用于衍生自仲胺的苯甲酰胺。通过使用已知绝对构型的氨基醇(1-4)和二胺(5、6)的苯甲酰基衍生物,我们证明了由于仲和叔苯甲酰胺引起的250-210 nm范围激子棉花效应通常相反。如半经验分子模型和NMR数据所示,这种差异的根源可追溯到仲,叔苯甲酰胺中酰胺CN键的不同构象平衡。由于叔苯甲酰胺的激子偶合,该特征可用于通过分析CD光谱确定绝对构型。