吡咯烷并手性噁唑硼烷催化芳香酮的不对称还原机理的量子化学研究

不对称催化还原;吡咯烷并手性噁唑硼烷催化芳香酮的不对称还原机理的量子化学研究     

苯甲酮不对称还原反应的理论研究

本文用AM1分子轨道方法研究了1,3,2-噁唑硼烷对苯甲酮的不对称催化还原.反应经历了噁唑硼烷-硼烷配合物的形成及其与苯甲酮的结合、氢转移及脱去噁唑硼烷形成手性产物二级醇-硼烷配合物四步过程.获得了各步的反应热、速度控制步骤的过渡态结构和位能曲线及其相应的反应活化能,计算发现反应机理中的第3步氢转移产物有四员环结构特征.     

亚胺不对称催化还原的量子化学研究

对手性噁唑硼烷催化亚胺不对称还原反应进行了量子化学研究. 对反应中间体和过渡态进行了B3LYP/6-31G(d)全优化. 噁唑硼烷对亚胺还原的催化作用是显著的. 还原反应经历了催化剂-硼烷加合物、催化剂-硼烷-亚胺加合物、催化剂-氨基硼烷加合物的生成, 以及催化剂-氨基硼烷加合物的离解并再生催化剂等过程. 还原反应的速度控制步骤是噁唑硼烷-氨基硼烷加合物的离解. 理论预测的还原产物是与实验吻合的R-手性胺.     

手性氨基醇催化的前手性芳酮的不对称还原反应

首次以天然D-樟脑的衍生物为原料, 合成了两个新型龙脑基氨基醇配体, 研究了它们与硼烷原位制备成手性噁唑硼烷后, 在不对称催化氢化还原前手性芳酮中的性能, 得到的手性仲醇的对映体过量(ee)值最高可达96%, 还考察了反应温度、时间、溶剂等因素对苯乙酮的不对称氢化还原的化学产率和光学收率的影响.     

手性噁唑硼烷催化的烷基(4-二烷基氨基)苯基酮的不对称硼烷还原

在手性硼杂噁唑烷催化下，用硼烷不对称还原了一系列烷基4-二烷基氨基苯基酮，结果表明由于存在催化剂和硼烷中的硼原子与氮原子的强络合作用，在该不对称还原中，该类酮比相应的烷基4-烷基、4-烷氧基、4-烷硫基酮表现出了较明显的取代基对对映选择性的影响。     

手性噁唑硼烷的研究进展及其应用

手性噁唑硼烷是不对称合成的重要催化剂, 它可以高产率、高立体选择性地催化酮、内消旋酰亚胺以及亚胺的不对称还原, 催化立体选择性Diels-Alder反应、不对称Mukaiyama缩合反应等重要有机化学反应. 概述了近十年来手性噁唑硼烷在不对称合成中的研究进展以及在合成VB₁₂等多种天然及非天然活性化合物中的应用.     

手性噁唑硼烷结构与还原苯基乙基甲酮的对映选择性研究~≠

本文以苯基乙基甲酮为还原底物,研究了原地(in situ)制备的在3、4、5位具有不同取代基的手性1,3,2-(口恶)唑硼烷催化剂的结构与不对称催化效应关系。研究结果表明,在不对称催化硼烷还原反应中(CBS方法),产物的构型和对映选择性主要受手性(口恶)唑硼烷的4位取代基控制。     

噁唑硼烷催化前手性酮不对称还原反应机理的量子化学研究

对手性噁唑硼烷催化3,3-二甲基丁酮-2不对称还原反应机理进行了从头算研究.结果表明,该不对称还原反应是放热的.反应经历了催化剂-硼烷加合物、催化剂-硼烷-酮加合物、含B-O-B-N四元环的催化剂-烷氧基硼烷加合物的生成,以及催化剂-烷氧基硼烷加合物的离解并再生催化剂等过程.在催化剂-硼烷-酮加合物经氢转移而生成催化剂-烷氧基硼烷加合物的过程中,氢转移与B-O-B-N四元环的形成是协同进行的.氢转移是还原反应的控制步骤.氢转移过渡态具有扭曲的椅式结构,所决定的还原产物是与实验相吻合的R手性醇.     

手性2-噁唑烷酮的无溶剂合成法

手性2-噁唑烷酮的无溶剂合成法;手性氨基醇;脲;手性噁唑烷酮     

不对称硼烷还原合成手性氨基醇

用原位生成的手性噁唑硼烷为催化剂,用2molBH3对1molα 或β 氨基酮进行了对映选择性还原,生成光学活性氨基醇 硼烷络合物,后者脱去BH3后给出光学活性氨基醇,ee值最高达99%.讨论了氨基酮结构与反应选择性的关系.     

取代基对手性唑噁唑硼烷催化还原苯基乙基酮对映体选择性影响的理论研究

用AM1方法和过渡态理论研究了取代基对含侧链手性噁唑硼烷催化还原苯 基乙杂程逖≡裥缘挠跋欤扑憬峁砻鳎杂逞≡裥匀【鲇?R)和(S)两个对映体? 叫蟹从Φ乃俾食Ｊ龋盋(4)和C(5)位上的取代基呈顺式时，所得对映体以(R) 型为主．对映选择性的高低与噁唑硼烷环上不同位置原子连接的取代基基团的大? ∮泄兀扑憬峁胧笛樽芙岢龅慕崧巯辔呛希? $601 $AThe influence of substituents on the enantioselectivity in asymmetric branched-oxazaborolidine-catalyzed reductions of phenyl- ethyl ketone has been studied by using AMI MO method and transition state theory. The results show that the enantioselectivity is determined by the ratio of the rate constants of two parallel reactions conducting to spatial configurations (R) and (S). When the substituents connecting with C(4) and C(5) are in cis-form the reduction products of phenyl-ethyl ketone in the reactions are mainly of configuration ( R). In asymmetric boron-catalyzed reduction reactions the higher or lower magnitude for enantioselectivity and reaction barrier are governed by various substituents connecting with atoms of oxazaborolidine ring. The computational results are in consistence with experiments.     

Asymmetric reduction of representative ketones with a bis-chiral oxazaborolidine system

In recent years, many optically active β-amino alcohols, mostly derived from naturally occurring α-amino acids, have been incorporated into the asymmetric synthesis as chiral auxiliaries or ligands.1 An effective asymmetric catalysts, the oxazaborolidine-borane reagents, which were originally pioneered by Itsuno and Corey,2 were generally prepared from chiral β-amino alcohols by the reaction with boric acid or formed in situ in the presence of borane. These reagents provide excellent enanti…     

Quantum chemical modeling of chiral catalysis. Part 8. On the conformational freedom of the ketone of ketone-borane complexes of oxazaborolidines used as catalysts in the enantioselective reduction of ketones

Standard ab initio molecular orbital methods were employed to study conformational freedom of the ketone of ketone-borane complexes of chiral oxazaborolidines used as catalysts for the enantioselective reduction of ketones (CBS reduction). A formaldehyde-borane complex of 1,3,2-oxazaborolidine was used as a model system. A new conformation was found which was energetically more advantageous than the original one predicted by Corey et al. The new conformation was predicted to be destabilized by bulky substituents at the C-5 of the ring. A new class of potential oxazaborolidine catalysts for the enantioselective reduction of ketones was invented.     

A convenient method for the preparation of oxazaborolidine catalyst in situ using (S)-α,α-diphenylpyrrolidinemethanol,tetrabutylammonium borohydride,and methyl iodide for the asymmetric reduction of prochiral ketones

An oxazaborolidine catalyst is readily prepared in situ at 25 °C in THF using (S)-α,α-diphenylpyrrolidinemethanol and borane generated from tetrabutylammonium borohydride/CH₃I reagent system. The oxazaborolidine/BH₃ reagent system prepared in this way is useful for the reduction of prochiral ketones to the corresponding alcohols with up to 99% ee.     

Quantum chemical study on enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine. Part 1. Structures of catalyst–borane–keto oxime ether adducts

In the present work, quantum chemical computations of the enantioselective reduction of keto oxime ether with borane catalyzed by chiral oxazaborolidine are performed by means of the Hartree–Fock and the density functional methods. The structures of oxazaborolidine, oxazaborolidine–borane adduct, and oxazaborolidine–borane–keto oxime ether adducts are optimized completely at the HF/6‐31g* and B3LYP/6‐31g* levels and their properties studied in detail. The oxazaborolidine catalyst is a twisted chair structure and reacts with borane at the nitrogen site of the catalyst to form the catalyst–borane adduct whose formation reaction is exothermic. The catalyst–borane adduct reacts easily with keto oxime ether to form catalyst–borane–keto oxime ether adducts that have eight stable structures. The coordination of the carbonyl oxygen in keto oxime ether at the boron site of the catalyst is of more advantage to the enantioselective reduction of keto oxime ether than the coordination of the oxime nitrogen in the keto oxime ether at the boron site is. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 291–304, 2001     

Highly catalytic enantioselective reduction of aromatic ketones using chiral polymer-supported Corey,Bakshi, and Shibata catalysts

A systematic study was conducted to formulate the optimal reaction parameters for polymer-supported (PS)-oxazaborolidine catalyzed enantioselective ketone reduction. The B-methylated chiral oxazaborolidine prepared in situ from the previously reported polymers by Degni et al. have been used in the enantioselective borane reduction of some substituted aromatic ketones to afford the corresponding optical active secondary alcohol products. While the linear-bound system shows low enantioselectivity, the cross-linked version affords enantioselectivities almost identical to those of the monomeric model (with up to 96% enantiomeric excesses).     

Quantum chemical study on asymmetric catalysis reduction of imine

The asymmetric catalysis reaction is considered to be an important way by which chiral compounds are generated. Chiral 1,3,2-oxazaborolidine, as an effective asymmetric catalyst, is used widely in the enantioselective reduction of prochiral ketones, imines, and carbon-carbon double bonds[1—3]. Up to now, a number of quantum chemical modeling investigations of the en-antioselective reduction of prochiral ketones with borane catalyzed by chiral oxazaborolidines have been carried out[4—7]. Howe…     

Total synthesis of peumusolide A, NES non-antagonistic inhibitor for nuclear export of MEK

The first total synthesis of peumusolide A (1) has been achieved by combination of regio- and stereo-selective aluminum-mediated hydroiodination to 2-yn-1-ol and enantioselective reduction of 4-en-1-yn-3-one with the chiral oxazaborolidine as the key reactions. This total synthesis has unequivocally established our proposed absolute structure of 1.