Catalytic Hydrogenation of Chiral α-Amino and α-Hydroxy Esters at Room Temperature with Nishimura Catalyst without Racemization
摘要:
The hydrogenation or carboxylic acid derivatives at room temperature was investigated. With a mixed Rh/Pt oxide (Nishimura catalyst), low to medium activity was observed for various alpha-amino and alpha-hydroxy esters. At 100 bar hydrogen pressure and 10% catalysts loading, high yields or tire desired amino alcohols and diols were obtained without racemization. The most suitable alpha-substituents were NH2, NHR, and 011, whereas beta-NH2 were less effective. Usually, aromatic rings were also hydrogenated, but with the free bases of amino acids as substrates, some selectivity was observed. No reaction was round for alpha-NR2, alpha-OR, and unfunctionalized esters; acids and amides, were also not reduced under these conditions. A working hypothesis for the mode or action of the catalyst is presented.
The Efficient Synthesis of Alkoxy-esters from Hydroxy Carboxylic Acids Using Dimsyllithium in Dimethylsulfoxide Followed by Alkylation with an Alkyl Halide
Hydroxy acids are converted directly into the related alkyl ether-alkyl esters in high yields in a single operation by double deprotonation using dimsyllithium in dimethylsulfoxide followed by treatment with an alkyl halide.
Stereoselective Ketone Rearrangements with Hypervalent Iodine Reagents
作者:Florence Malmedy、Thomas Wirth
DOI:10.1002/chem.201603022
日期:2016.11.2
The first stereoselective version of an iodine(III)‐mediated rearrangement of arylketones in the presence of orthoesters is described. The reaction products, α‐arylated esters, are very useful intermediates in the synthesis of bioactive compounds such as ibuprofen. With chiral lactic acid‐based iodine(III) reagents product selectivities of up to 73 % ee have been achieved.
Enantiomerically pure 2-(1-hydroxyalkyl)pyridines were prepared via reaction of 2-lithiopyridine with (R)-2,3-O-isopropylideneglyceraldehyde, methyl (S)-2-methoxypropionate and methyl (S)-2-methoxy-2-phenylacetate, obtained from D-mannitol, L-lactic acid and L-mandelic acid, respectively. 6,6′-Bis(1-hydroxyalkyl)-2,2′-bipyridines were obtained from the same naturally occurring chiral compounds and 2-bromo-6-lithiopyridine with subsequent Ni-catalysed coupling.
通过 2-硫代吡啶与(R)-2,3-O-异亚丙基甘油醛、(S)-2-甲氧基丙酸甲酯和(S)-2-甲氧基-2-苯基乙酸甲酯的反应,制备了对映体纯度较高的 2-(1-羟基烷基)吡啶,这些对映体分别来自 D-甘露醇、L-乳酸和 L-扁桃酸。6,6′-双(1-羟基烷基)-2,2′-联吡啶是由相同的天然手性化合物和 2-溴-6-硫代吡啶经 Ni 催化偶联得到的。
Hydrophilic Oligo(lactic acid)s Captured by a Hydrophobic Polyaromatic Cavity in Water
owing to effective hydration. Nevertheless, herein we report that the hydrophobic cavity of a polyaromatic capsule, formed through coordination‐driven self‐assembly, can encapsulate hydrophilic oligo(lactic acid)s in water with relatively high binding constants (up to Ka=3×105 m−1). X‐ray crystallographic and ITC analyses revealed that the unusual host–guest behavior is caused by enthalpic stabilization
由于有效的水合作用,与生物有关的亲水性分子很少与水中的疏水性化合物和表面相互作用。然而,本文我们报道通过配位驱动的自组装形成的聚芳族胶囊的疏水腔可以以较高的结合常数(高达K a = 3×10 5 m)包封亲水性低聚乳酸。-1)。X射线晶体学和ITC分析表明,不寻常的主客体行为是由CH-π和氢键相互作用引起的焓稳定作用引起的。所述多芳族腔稳定可水解的环状二(乳酸),并且即使在水中也优先从低聚(乳酸)的混合物中捕获四(乳酸)。
Ether-directed diastereoselectivity in catalysed Overman rearrangement: comparative studies of metal catalysts
作者:Ieva Jaunzeme、Aigars Jirgensons
DOI:10.1016/j.tet.2008.03.099
日期:2008.6
Ether-directed diastereoselectivity in Overman rearrangement of delta-methoxy and delta-TBDMSO substituted allylic trichloroacetimidates has been explored using PtCl2, PtCl4, AuCl and AuCl3 catalysts in comparison with commonly used Pd(II) catalysts. For both substrates the use of PtCl2 catalyst gave notably improved anti/syn-ratio of 1,2-aminoalcohol derivatives (anti/syn=11:1 for 5-methoxy; 6:1 for delta-TBDMSO) compared to all metal catalysts known to promote Overman rearrangement. Formation of 2-trichloromethyloxazoline was observed as a dominant side reaction in the metal catalysed rearrangement of a-methoxy substituted allylic trichloroacetimidates considerably reducing the yield of the desired product. This side reaction was suppressed when delta-TBDMS-ether was used as a directing group. (C) 2008 Elsevier Ltd. All rights reserved.