Remarkably Efficient Enantioselective Titanium(IV)−(<i>R</i>)-H<sub>8</sub>-BINOLate Catalyst for Arylations to Aldehydes by Triaryl(tetrahydrofuran)aluminum Reagents
作者:Kuo-Hui Wu、Han-Mou Gau
DOI:10.1021/ja062080y
日期:2006.11.1
Novel asymmetric triarylaluminum AlAr3(THF) additions to aldehydescatalyzed by 10 mol % of the titanium(IV) complex of (R)-H8-BINOL ligand are reported. The catalytic system is extremely efficient with reactions completing within 10 min. The system applies to the most diversified aldehydes to date, and more than 20 aldehydes were examined to afford diarylmethanols having an electron-donating or an
Enantioselective Allylic Substitution Catalyzed by Chiral [Bis(dihydrooxazole)]palladium Complexes: Catalyst structure and possible mechanism of enantioselection
作者:Peter Von Matt、Guy C. Lloyd-Jones、Alexander B. E. Minidis、Andreas Pfaltz、Ludwig Macko、Markus Neuburger、Margareta Zehnder、Heinz Rüegger、Paul S. Pregosin
DOI:10.1002/hlca.19950780202
日期:1995.3.22
containing the same bis(dihydrooxazole) ligand, were characterized by X-ray structure analysis and by NMR spectroscopy in solution. The structural data reveal that steric interactions of the allyl system with the chiral ligand result in selective electronic activation of one of the allylic termini. The higher reactivity of one allylic terminus toward nucleophilic attack is reflected in a significantly longer
研究了具有手性双(二氢恶唑)配体的烯丙基钯配合物,作为rac -1,3-二苯基丙-2-烯基乙酸酯(rac - 5)与丙二酸二甲酯的阴离子的对映选择性烯丙基取代反应的催化剂(方案1)。使用对映体纯的(S,E)-1-(4-甲苯基)-3-苯基丙-2-烯基苯甲酸((S)-25)作为底物,表明反应是通过乙酸的' syn '置换法进行的由丙二酸二甲酯制得(方案6)。的[钯11(η 3 -烯丙基)]络合物18和类似的[将Pd(η都含有相同的双(二氢恶唑)配体的3 -1,3-二苯基烯丙基)]络合物20通过X-射线结构分析和溶液中的NMR光谱表征。结构数据表明烯丙基系统与手性配体的空间相互作用导致烯丙基末端之一的选择性电子活化。一个烯丙基末端对亲核攻击的更高反应性反映在明显更长的PdC键和相应的13 C-NMR共振向更高频率的偏移上。
[2,3]-Wittig Rearrangement of Enantiomerically Enriched 3-Substituted 1-Propenyloxy-1-phenyl-2-propen-1-yl Carbanions: Effect of Heteroatoms and Conjugating Groups on Planarization of an α-Oxy-Benzylcarbanion through a Double Bond
Don't get trapped: The effect of conjugating electron‐withdrawing groups and α‐anion‐stabilizing heteroatom substituents on configurational stability of chiral carbanions through a double bond was examined on the basis of extent of chirality transfer in intramolecular trapping in [2,3]‐Wittig rearrangement of chiral 3‐substituted 1‐propenyloxy‐1‐phenyl‐2‐propen‐1‐yl carbanions (see scheme).
Alkenylboronates were used as a vinyl source in the asymmetric addition of an alkenylzinc reagent to aldehydes catalyzed by a dendritic ligand. The resulting allylic alcohol products were obtained in 66–96% ee and 35–64% yields.
and efficient access to polysubstituted chiral α-trifluoromethyl amines bearing two adjacent stereocenters and one allyl group in high yields with excellent regio-, diastereo-, and enantioselectivity. Importantly, this method also provides a powerful strategy for the synthesis of both regioisomeric products and the regioselectivity is controlled by the chiral catalysts and optically active substrates