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1.
Lewis acid catalyzed asymmetric halohydrin reactions—(halohydroxylation as well as halomethoxylation) of chiral α,β-unsaturated carboxylic acid derivatives were performed using N-halosuccinimide (NXS; X = Br, I) as the halogen source. Regio- and anti-selectivity of 100% and moderate to good diastereoselectivity with good yields were observed when Oppolzer’s sultam was used as the chiral auxiliary. Among the Lewis acids, Yb(OTf)3 was found to be the best catalyst. Alkenoyl and cinnamoyl substrates smoothly underwent bromohydrin reactions and the more electron-rich cinnamoyl substrates preferred to undergo iodohydrin reactions. However, electron-deficient cinnamoyl substrates did not respond to this Lewis acid catalyzed halohydrin reaction with NXS (X = Cl, Br, I). 相似文献
2.
Reversal of enantioselectivity in asymmetric Henry reactions was achieved with novel chiral C2-symmetric salen ligands bearing morpholine moieties by changing the Lewis acid center from Co(II) to Yb(III). The possible transition state models were supported by mass spectrometry experiments. 相似文献
3.
Joanna Jankowska 《Tetrahedron letters》2006,47(30):5281-5284
Among various transition metals, iron is nontoxic, cheap and hence of great potential synthetic use. We report herein a water stable chiral Lewis acid containing an iron(II) ion and a pybox-type ligand. The resulting cationic aqua complex of C2-symmetry is an effective Lewis acid catalyst for asymmetric Mukaiyama-aldol reactions in aqueous media. The aldol products have been obtained in good yields, syn-diastereoselectivities and ca. 70% levels of enantioselectivity. 相似文献
4.
Zi-Bo Li 《Tetrahedron letters》2005,46(13):2223-2226
The BINOL-salen compound (S)-5c in combination with Ti(OiPr)4 is found to catalyze the addition of TMSCN to aldehydes to form chiral cyanohydrins with very good enantioselectivity (75-85% ee). The reactions are carried out in one-pot at room temperature without the need to isolate the chiral Lewis acid catalyst. 相似文献
5.
Emmanuel Lacte Philippe Renaud 《Angewandte Chemie (International ed. in English)》1998,37(16):2259-2262
New prospects for synthetic applications are offered by the 1,2-acyloxy shift of β-(acyloxy)alkyl radicals, which proceeds with high yields under Lewis acidic conditions [Eq. (1)]. With the exception of cyclizations, this is the first Lewis acid mediated acceleration of a radical rearrangement. 相似文献
6.
Asymmetric allylation polymerization of bis(allylsilane) and dialdehyde containing Siphenyl linkage
《Tetrahedron: Asymmetry》2001,12(18):2509-2516
Repetitive Sakurai–Hosomi allylation between dialdehyde and bis(allylsilane) yielded a polymer having stereogenic carbons in its main chain. In the presence of an enantiopure Lewis acid catalyst such as chiral (acyloxy)borane (CAB), the allylation polymerization proceeded in a stereoselective manner to give optically active polymers. We have prepared new monomers containing Siphenyl linkages for the asymmetric allylation polymerization. After polymerization, the Siphenyl linkages in the main chain could be cleaved easily to give the corresponding chiral homoallylic alcohol. The enantiomeric purity of the chiral polymer was then evaluated by chiral HPLC analysis of the alcohol obtained from the degradation. 相似文献
7.
A highly enantioselective organozinc (R2Zn) addition to a series of aldehydes and ketones was developed based on conjugate Lewis acid–Lewis base catalysis. Optically active secondary and tertiary alcohols were obtained in high yields with high enantioselectivities without Ti(IV) compounds. Bifunctional chiral 3,3′‐diphosphoryl‐BINOL ligands were designed and prepared through a phospho‐Fries rearrangement as a key step. On the other hand, bifunctional chiral phosphoramide ligands were designed and prepared from L ‐valine. Mechanistic studies were performed by X‐ray analyses of Zn(II) cluster and chiral ligands, a 31P NMR experiment on Zn(II) complexes, and stoichiometric reactions with some chiral or achiral Zn(II) complexes to propose a transition state assembly that includes monomeric active intermediates. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 143–155; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20146 相似文献
8.
《Tetrahedron letters》2004,45(28):5379-5382
Stereoselectivity of the titanium-mediated aldol process based on (S)-2-benzyloxy-3-pentanone, 1, is dramatically modified by the presence of a Lewis acid. Among the Lewis acids surveyed, TiCl4 has given access to the corresponding 2,4-anti-4,5-syn aldol adducts with the highest diastereomeric ratios. The excellent stereocontrol exerted by the aforementioned ketone has been demonstrated in double asymmetric reactions involving chiral α-methyl-β-OTBDPS aldehydes. 相似文献
9.
Organorhenium(VII) and organomolybdenum(VI) oxides: synthesis and application in oxidation catalysis
Fritz E. Kühn Ana M. Santos Isabel S. Gonalves Carlos C. Romo Andr D. Lopes 《应用有机金属化学》2001,15(1):43-50
Methyltrioxorhenium(VII) has found numerous applications in various catalytic processes. In olefin epoxidation its activity can be enhanced by the addition of aromatic Lewis base nitrogen donor ligands, e.g. pyridines and pyrazoles. Due to the comparatively weak coordination of these ligands, a significant excess has to be used. Therefore the MTO/chiral Lewis base/H2O2 system is not very useful for chiral epoxidations. In contrast to this, dimethyldioxomolybdenum(VI) MoO2(CH3)2 undergoes a significantly stronger interaction with Lewis bases and seems, despite its generally somewhat lower activity, a reasonable candidate for application in chiral epoxidation reactions together with an appropriate chiral Lewis base ligand. Complexes of the type MoO2(CH3)2L are accessible via MoO2X2L (X = Cl, Br). These latter compounds are even more active in olefin epoxidation than MoO2(CH3)2L. Unfortunately, however, all the Mo(VI) complexes mentioned above need t‐butyl hydroperoxide as oxidizing agent and do not show activity in the presence of H2O2. 相似文献
10.
Rei Tomifuji Prof. Takuya Kurahashi Prof. Seijiro Matsubara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(38):8987-8991
The development and use of a multiple-activation catalyst with ion-paired Lewis acid and Brønsted acid in an asymmetric aza-Diels–Alder reaction of simple dienes (non-Danishefsky-type electron-rich dienes) was achieved by utilizing the [FeBr2]+[FeBr4]− combination prepared in situ from FeBr3 and chiral phosphoric acid. Synergistic effects of the highly active ion-paired Lewis acid [FeBr2]+[FeBr4]− and a chiral Brønsted acid are important for promoting the reaction with high turnover frequency and high enantioselectivity. The multiple-activation catalyst system was confirmed using synchrotron-based X-ray absorption fine structure measurements, and theoretical studies. This study reveals that the developed catalyst promoted the reaction not only by the interaction offered by the ion-paired Lewis acid and the Brønsted acid but also noncovalent interactions. 相似文献
11.
Highly enantioselective (96% ee) and endo-selective (>99:1) cycloaddition reactions were observed between carbonyl ylides, generated from o-(p-bromobenzyloxy)carbonyl-α-diazoacetophenone, and 3-crotonoyl-2-oxazolidinone using (4S,5S)-Pybox-4,5-Ph2-Yb(OTf)3 (20 mol %) as the chiral Lewis acid catalyst. In contrast, high exo-selectivity (exo/endo=82:18; 96% ee, exo) was observed for the reaction of o-methoxycarbonyl-α-diazoacetophenone with 3-acryloyl-2-oxazolidinone under similar conditions as reported previously. In the case of cycloaddition reactions between 2-benzopyrylium-4-olate, generated from o-methoxycarbonyl-α-diazoacetophenone, and 3-cinnamoyl- or 3-[(E)-3-(ethoxycarbonyl)propenoyl]-2-oxazolidinones, using the same chiral Lewis acid, the reaction favored the endo-adduct with relatively good enantioselectivity (72 and 78% ee, respectively). 相似文献
12.
The LBAs (Lewis acid-assisted Brønsted acid catalysis) is proposed as possible mechanistic process in the simple FeCl3-catalyzed Michael reactions of chalcones with active methylene compounds in organic solvents. And iron salts were found to be effective promoters in the asymmetric Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketone, which resulted in excellent yield and high level of enantioselectivity (up to 91% ee) in the presence of low catalytic amount of iron and simple chiral primary amine. 相似文献
13.
《Tetrahedron: Asymmetry》2007,18(18):2129-2132
An enantioselective silylphosphination of aldehydes mediated by a chiral Lewis acid is described. The chiral Lewis acid prepared from TiCl4 and diisopropyl l-tartrate successfully induced chirality in the addition of silylphosphine to several aldehydes, to give the corresponding α-hydroxyalkylphosphine derivatives in good yields and good enantioselectivities. 相似文献
14.
Trinadh Kaicharla Tony Roy Manikandan Thangaraj Dr. Rajesh G. Gonnade Dr. Akkattu T. Biju 《Angewandte Chemie (International ed. in English)》2016,55(34):10061-10064
Lewis acid‐catalyzed reactions of 2‐substituted cyclopropane 1,1‐dicarboxylates with 2‐naphthols is reported. The reaction exhibits tunable selectivity depending on the nature of Lewis acid employed and proceed as a dearomatization/rearomatization sequence. With Bi(OTf)3 as the Lewis acid, a highly selective dehydrative [3+2] cyclopentannulation takes place leading to the formation of naphthalene‐fused cyclopentanes. Interestingly, engaging Sc(OTf)3 as the Lewis acid, a Friedel–Crafts‐type addition of 2‐naphthols to cyclopropanes takes place, thus affording functionalized 2‐naphthols. Both reactions furnished the target products in high regioselectivity and moderate to high yields. 相似文献
15.
In a rational chiral molecular design of chalcogenides, optically active thiepin with C2‐symmetric chirality was synthesized from commercially available thiophene. Then enatioselective Chalcogeno‐Baylis‐Hillman reactions of arylaldehydes with methyl vinyl ketone (MVK) and acrylates were investigated in the presence of thiepin‐Lewis acid complex. Finally, up to 64% ee was achieved in the presence of 0.2 equiv. of (S)‐thiepin at 20°C. 相似文献
16.
[2+2] Photocycloaddition of 3‐Alkenyloxy‐2‐cycloalkenones: Enantioselective Lewis Acid Catalysis and Ring Expansion
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M. Sc. Richard Brimioulle Prof. Dr. Thorsten Bach 《Angewandte Chemie (International ed. in English)》2014,53(47):12921-12924
By application of substoichiometric amounts (50 mol %) of a chiral Lewis acid, the intramolecular [2+2] photocycloaddition of the title compounds was achieved with high enantioselectivity (up to 94 % ee). Upon cleavage of the cyclobutane ring the resulting tricyclic products underwent ring‐expansion reactions under acidic conditions and formed anellated seven‐ or eight‐membered‐ring systems without racemization. The ring expansion could be combined with a diastereoselective reduction (triethylsilane) or allylation (allyltrimethylsilane) upon BF3 catalysis (48–87 % yield). 相似文献
17.
Xiying Zhang Wangbin Wu Weidi Cao Han Yu Xi Xu Prof. Dr. Xiaohua Liu Prof. Dr. Xiaoming Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4876-4880
Highly efficient asymmetric intermolecular radical-polar crossover reactions were realized by combining a chiral N,N′-dioxide/NiII complex catalyst with Ag2O under mild reaction conditions. Various terminal alkenes and indanonecarboxamides/esters underwent radical addition/cyclization reactions to afford spiro-iminolactones and spirolactones with good to excellent yields (up to 99 %) and enantioselectivities (up to 97 % ee). Furthermore, a range of different radical-mediated oxidation/elimination or epoxide ring-opening products were obtained under mild reaction conditions. The Lewis acid catalysts exhibited excellent performance and precluded the strong background reaction. 相似文献
18.
Prof. Michael North Marta Omedes‐Pujol Courtney Williamson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(37):11367-11375
The asymmetric addition of trimethylsilyl cyanide to aldehydes can be catalysed by Lewis acids and/or Lewis bases, which activate the aldehyde and trimethylsilyl cyanide, respectively. It is not always apparent from the structure of the catalyst whether Lewis acid or Lewis base catalysis predominates. To investigate this in the context of using salen complexes of titanium, vanadium and aluminium as catalysts, a Hammett analysis of asymmetric cyanohydrin synthesis was undertaken. When Lewis acid catalysis is dominant, a significantly positive reaction constant is observed, whereas reactions dominated by Lewis base catalysis give much smaller reaction constants. [{Ti(salen)O}2] was found to show the highest degree of Lewis acid catalysis, whereas two [VO(salen)X] (X=EtOSO3 or NCS) complexes both displayed lower degrees of Lewis acid catalysis. In the case of reactions catalysed by [{Al(salen)}2O] and triphenylphosphine oxide, a non‐linear Hammett plot was observed, which is indicative of a change in mechanism with increasing Lewis base catalysis as the carbonyl compound becomes more electron‐deficient. These results suggested that the aluminium complex/triphenylphosphine oxide catalyst system should also catalyse the asymmetric addition of trimethylsilyl cyanide to ketones and this was found to be the case. 相似文献
19.
The conjugate addition of amines is considered to be a useful reaction in synthetic organic chemistry. The reaction of reactive electrophilic olefins, ethenetricarboxylates, and aromatic amines with and without catalytic Lewis acids such as ZnCl2 and ZnBr2 at room temperature gave amine adducts in high yields. The products were converted to α-amino acid, dl-aspartic acid derivatives. Using Lewis acids such as Sc(OTf)3 and Zn(OTf)2 at higher temperature (40-80 °C), the reaction of ethenetricarboxylates and N-methylaniline gave an aromatic substitution product. A catalytic enantioselective conjugate addition using a chiral Lewis acid was also investigated. For example, the reaction of 1,1-diethyl 2-tert-butyl ethenetricarboxylate with N-methylaniline in the presence of chiral bisoxazoline-Cu(II) complex in THF at −20 °C for 17 h gave an amine adduct in 91% yield and 78% ee. On the other hand, the reaction with aniline and primary aniline derivatives gave adducts with almost no ee%. 相似文献
20.
Taichi Kano 《Tetrahedron letters》2006,47(6):873-875
A novel Sn(IV) aryloxide Lewis acid has been designed and prepared from SnCl4 and (S)-3,3′-bis(3,5-bis(trifluoromethyl)phenyl)-1,1′-bi-2-naphthol. The chiral Sn(IV) Lewis acid has been successfully applied to the enantioselective Diels-Alder reaction. 相似文献