- Combining prolinamides with 2-pyrrolidinone: Novel organocatalysts for the asymmetric aldol reaction
-
Peptides and especially prolinamides have been identified as excellent organocatalysts for the aldol reaction. The combination of prolinamides with derivatives bearing the 2-pyrrolidinone scaffold, deriving from pyroglutamic acid, led to the identification of novel organocatalysts for the intermolecular asymmetric aldol reaction. The new hybrids were tested both in organic and aqueous media. Among the compounds tested, 22 afforded the best results in petroleum ether, while 25 afforded the products in brine in high yields and selectivities. Then, various ketones and aldehydes were utilized and the products of the aldol reaction were obtained in high yields (up to 100%) with excellent diastereo- (up to 97:3 dr) and enantioselectivities (up to 99% ee).
- Vlasserou, Ismini,Sfetsa, Maria,Gerokonstantis, Dimitrios-Triantafyllos,Kokotos, Christoforos G.,Moutevelis-Minakakis, Panagiota
-
p. 2338 - 2349
(2018/04/06)
-
- The 4,5-methano-l-proline as a chiral organocatalysts in direct asymmetric aldol reactions
-
The 4,5-methano-l-proline was studied for the direct asymmetric aldol reaction of acetone or cyclohexanone with various aromatic and aliphaticaldehydes at -20 °C or 0 °C. A loading of only 5mol % of derivative 1a was employed in this catalytic system, and excellent enantioselectivities (up to 99% ee) and yields (up to 98% yield) could be achieved.
- Yu, Na,Han, Sheng,Yu, Han
-
p. 4665 - 4669
(2015/06/08)
-
- Highly enantioselective direct asymmetric aldol reaction catalyzed by 4,5-methano-L-proline
-
The 4,5-methano-L-proline was used as chiral organocatalysts in direct asymmetric aldol reactions. Under the optimal conditions, excellent enantioselectivities (up to 99% ee) were obtained with high chemical yields (up to 95%) for a series of aldehydes using only 5 mol% catalyst loading. To show the practicality of the method, the reaction was tested at a large scale. The reaction was complete in 16 h, and the aldol product was obtained in 86% yield and 93% ee.
- Zhang, Yukun,Zhu, Jun,Yu, Na,Yu, Han
-
supporting information
p. 171 - 174
(2015/03/04)
-
- Synthesis of sulphur-modified bifunctional hydrotalcites and study of their surface characteristics by inverse gas chromatography
-
In this study, various sulphur-modified hydrotalcite catalysts were prepared, and the influence of calcination temperature on their acid-base properties was investigated. Structural characterization of the catalysts was studied using X-ray powder diffraction, scanning electron microscopy, N2 physisorption, elemental analysis and Fourier transform infrared spectroscopy. The structural characterization indicated that the layer structure of all catalysts was retained but the specific surface areas were enlarged. Inverse gas chromatography was carried out to quantitatively determine the catalysts' acid-base properties by calculating the thermodynamic parameters, including dispersive surface free energy, adsorption free energy, adsorption enthalpy, and acid-base interaction constants. The results showed that the strength and content of acidic and alkaline sites were enhanced with increasing calcination temperature. Moreover, several typical aldol condensation reactions were selected to study the catalytic activity of the developed catalysts. The results showed that the sulphur-modified hydrotalcite catalysts possess high activity and good regenerability for typical aldol condensation reactions.
- Ren, Xiaoqian,Hu, Xi,Zhang, Feng,Wang, Junge,Liang, Jinhua,Wu, Wenliang,Jiang, Min,Wang, Jun
-
p. 4813 - 4820
(2015/10/05)
-
- Asymmetric Catalysis with Ethylene. Synthesis of Functionalized Chiral Enolates
-
Trialkylsilyl enol ethers are versatile intermediates often used as enolate surrogates for the synthesis of carbonyl compounds. Yet there are no reports of broadly applicable, catalytic methods for the synthesis of chiral silyl enol ethers carrying latent functionalities useful for synthetic operations beyond the many possible reactions of the silyl enol ether moiety itself. Here we report a general procedure for highly catalytic (substrate:catalyst ratio up to 1000:1) and enantioselective (92% to 98% major enantiomer) synthesis of such compounds bearing a vinyl group at a chiral carbon at the β-position. The reactions, run under ambient conditions, use trialkylsiloxy-1,3-dienes and ethylene (1 atm) as precursors and readily available (bis-phosphine)-cobalt(II) complexes as catalysts. The silyl enolates can be readily converted into novel enantiopure vinyl triflates, a class of highly versatile cross-coupling reagents, enabling the syntheses of other enantiomerically pure, stereodefined trisubstituted alkene intermediates not easily accessible by current methods. Examples of Kumada, Stille, and Suzuki coupling reactions are illustrated.
- Biswas, Souvagya,Page, Jordan P.,Dewese, Kendra R.,RajanBabu
-
supporting information
p. 14268 - 14271
(2015/12/01)
-
- Tuning the sense of product stereochemistry in aldol reactions of acetone and aromatic aldehydes in the presence of water with a single chiral catalyst
-
We report the aldol addition of acetone to aromatic aldehydes in the presence of a large amount of water where the stereochemical outcome of the reactions can be tuned with achiral salt additives using a single proline-derived catalyst. Depending on the nature of the added salt the (R) and (S) enriched products could be obtained. In the reaction of 2-nitrobenzaldehyde with acetone, NaOAc promoted the formation of the (S)-enantiomer (20% ee) while using NH4Cl the (R)-enantiomer was obtained in excess (58% ee). A similar inversion was observed for several other aromatic aldehydes.
- Gurka, András A.,Szori, Kornél,Szollosi, Gy?rgy,Bartók, Mihály,London, Gábor
-
supporting information
p. 7201 - 7205
(2015/12/12)
-
- Improved conditions for the proline-catalyzed aldol reaction of acetone with aliphatic aldehydes
-
The proline-catalyzed asymmetric aldol reaction between aliphatic aldehydes and acetone has, to date, remained underdeveloped. Challenges in controlling this reaction include avoiding undesired side reactions such as aldol condensation and self-aldolization. In recent years we have developed optimized conditions, which enable high yields and good to excellent enantioselectivities, and which are presented in this communication. Georg Thieme Verlag Stuttgart New York.
- Martínez, Alberto,Zumbansen, Kristina,D?hring, Arno,Van Gemmeren, Manuel,List, Benjamin
-
supporting information
p. 932 - 934
(2014/05/06)
-
- Unusual enantioselectivities in heterogeneous organocatalyzed reactions: Reversal of direction using proline di- versus tri-peptides in the aldol addition
-
The heterogeneous asymmetric direct aldol reactions between aldehydes (2-nitrobenzaldehyde, 2-methylpropanal) and ketones (acetone, cyclohexanone) in the presence of polystyrene (PS) resin supported di- and tripeptides were studied under otherwise identic
- Szollosi, Gy?rgy,Csámpai, Antal,Somlai, Csaba,Fekete, Mónika,Bartók, Mihály
-
-
- Reversal of enantioselectivity in aldol reaction: New data on proline/λ-alumina organic-inorganic hybrid catalysts
-
We report new results on the aldol reactions between aldehydes of three different types (aromatic, aliphatic and cycloaliphatic) and acetone/cycloalkanones as reaction partners, driven by organic-inorganic hybrid catalyst Pro/λ-Al2O3. In contrast to the homogeneous liquidphase reaction, over Pro/λ-Al2O 3reversal of the enantioselection in up to 20-40 % ee depending on the structure of the aldehyde was observed in reactions of acetone. Reversal of the ee in the presence of c-Al2O3cannot be generalized, as it has only been observed for acetone among the ketones studied by us. It was proven using methods of a great variety such as ultrasonic irradiation, reuse measurements on used catalyst and the filtrate of the first reaction, measurements on the L-Pro-L-Pro(OH) dipeptide, studies using mixtures of L-Pro and D-Pro that the organic-inorganic hybrid catalyst Pro/λ-Al 2O3formed in situ is responsible for reversal of the ee. In the reactions of cycloalkanones there is presumably competition between the liquid-phase and the surface reaction over Pro/ c-Al2O 3with preference for the former. Based on these results a surface reaction pathway was proposed. Although, the ees obtained under heterogeneous catalytic conditions are low, further studies may lead to application of this unusual phenomenon for obtaining chiral heterogeneous catalysts suitable for the preparation of the desired enantiomer of a chiral compound using the same chiral source. Springer Science+Business Media New York 2013.
- Sz?ll?si, Gyo?rgy,Fekete, Mónika,Gurka, András A.,Bartók, Mihály
-
p. 478 - 486
(2014/06/24)
-
- Reversal of the enantioselectivity in aldol addition over immobilized di- and tripeptides: Studies under continuous flow conditions
-
Heterogeneous asymmetric direct aldol reactions between aldehydes (2-nitrobenzaldehyde, 2-methylpropanal) and acetone catalyzed by polystyrene resin (PS) supported di- and tripeptides H-Pro-Pro-, H-Pro-Pro-Pro-, H-Pro-Glu(OH)-, H-Pro-Pro-Glu(OH)-, H-Pro-Asp(OH)-, H-Pro-Pro-Asp(OH)-, H-Ser-Glu(OH)-, H-Ser-Ser-Glu(OH)-, H-Val-Glu(OH)-, H-Val-Val-Glu(OH)-MBHA-PS, were studied under identical experimental conditions at room temperature in a continuous-flow fixed-bed reactor (CFBR) system. In the asymmetric aldol reactions reversal of enantioselectivity was observed on H-Pro-Pro-Glu(OH)- and H-Pro-Pro-Asp(OH)-MBHA-PS-supported catalysts (ee 42-67% S) as compared to the H-Pro-Glu(OH)- and H-Pro-Asp(OH)-MBHA-PS-supported catalyst (ee 28-82% R). In the case of H-Pro-Pro- and H-Pro-Pro-Pro-MBHA-PS-supported catalysts reversed enantioselectivity was observed by using the benzoic acid additive (12% S) as compared to the H-Pro-MBHA-PS catalyst (25% R). The stability of the catalysts in the flow system was consistent with the heterogeneous character of the reaction, as was the linear behavior obtained using mixtures of l- and d-enantiomers of the supported H-Pro-MBHA-PS catalyst. The enamine character of the reaction intermediates was supported by ESI-MS measurements. Based on these and the computed structure of the peptides, the conformation of the intermediate adducts is held responsible for chiral induction, therefore for the enantioselectivity inversion observed in these reactions.
- Gurka, Andrs,Bucsi, Imre,Kovcs, Lenke,Szollosi, Gy?rgy,Bartk, Mihly
-
p. 61611 - 61618
(2015/02/19)
-
- Total synthesis and conformational analysis of apratoxin C
-
Total synthesis of apratoxin C, a cyanobacterial cyclodepsipeptide with highly potent cytotoxicity against some cancer cell lines, was achieved using the apratoxin A synthetic strategy developed by us. To elucidate the relationship between conformation and activity, the tertiary structure of apratoxin C was analyzed by NMR spectroscopy. We obtained 37 ROEs and five 3JH,H values, which were translated into distance and dihedral angle constraints, respectively. Molecular modeling was performed with a restrained conformational search by a distance geometry method. The lowest energy structure indicated that the methyl group at C37 and the isopropyl group at C39 play critical roles in maintaining the conformation, whereas the methyl group at C34 does not. Moreover, we confirmed that apratoxin A and C possess similar conformations, providing a likely explanation for their nearly equivalent cytotoxicities.
- Masuda, Yuichi,Suzuki, Jun,Onda, Yuichi,Fujino, Yuta,Yoshida, Masahito,Doi, Takayuki
-
p. 8000 - 8009
(2015/03/18)
-
- Asymmetric aldol reactions in caprolactam-quaternary ammonium salt coordination ionic liquid catalyzed by L-Pro-L-Trp
-
A direct asymmetric aldol reaction of aldehydes and acetone catalyzed by L-Pro-L-Trp was performed in β-caprolactam-quaternary ammonium salt coordination ionic liquid media in the presence of N-methylmorpholine (NMM) in high yield and with good enantioselectivity. The approach has the advantages of simple product isolation, and reusable catalyst and coordination ion liquids. Copyright
- Zhang, Bao-Hua,He, Jing-Yu,Liu, Si-Jie,Shi, Lan-Xiang
-
p. 1266 - 1268
(2013/08/23)
-
- A novel trifunctional organocatalyst for the asymmetric aldol reaction: A facile enantioselective synthesis of β-hydroxyketones
-
A new l-prolinamide trifunctional catalyst has been developed for the enantioselective aldol reaction of various aromatic and aliphatic aldehydes with acetone. This method provides high yields of β-hydroxyketones (up to 90%) with good enantioselectivity (up to 92%) at a low catalyst loading (10 mol %).
- Subba Reddy,Bhavani,Raju,Yadav
-
experimental part
p. 881 - 886
(2011/08/09)
-
- A flexible synthesis of C33-C39 polyketide region of apratoxin: Synthesis of natural and unnatural analogues
-
A flexible synthesis sequence toward the synthesis of the polyketide region of apratoxin has been developed. The common step of the synthesis is a crotylation reaction. Stereospecific aldolisation, sulfate ring opening or Jacobsen HKR is also highlighted. This synthetic scheme led to the synthesis of several analogues. These examples raise the possibility of synthesising numerous analogues of this portion of apratoxins. Then, together with our supported strategy to synthesise the oxazoline analogue of apratoxin A, this paper opens the possibility to provide easily oxoapratoxin analogues for future SAR studies of this potent antitumoral compound.
- Gilles, Arnaud,Martinez, Jean,Cavelier, Florine
-
scheme or table
p. 437 - 440
(2012/03/22)
-
- Renaissance of traditional organic reactions under microfluidic conditions: A new paradigm for natural products synthesis
-
Continuous flow synthesis for bioactive natural products is described. Efficient procedures using the microfluidic system were developed for the large-scale synthesis of important synthetic units of asparagine-linked oligosaccharide in glycoprotein. Advantageous aspects of microfluidic conditions, i.e., efficient mixing, fast heat transfer, and residence time control led to cation-mediated reactions, such as a-sialylation, β-mannosylation, and reductive opening of the benzylidene acetal groups in high yields. Microfluidic dehydration was developed for the industrial-scale synthesis of the immunostimulating natural terpenoid, pristane. The base-mediated aldol condensation in an aqueous biphasic system enabled the multigram synthesis of β-hydroxyketones in high yields. 2009 American Chemical Society.
- Tanaka, Katsunori,Fukase, Koichi
-
experimental part
p. 983 - 990
(2010/04/22)
-
- Efficient aldol condensation in aqueous biphasic system under microfluidic conditions
-
A microfluidic system was applied to aldol reaction in aqueous biphasic medium. Advantageous aspects of microfluidic conditions, that is, efficient mixing, fast heat transfer, and residence time control led to the high-yielding reaction of acetone enolate with even α-proton-containing aldehydes in biphasic aqueous-acetone system, by minimizing the formation of self-condensation products.
- Tanaka, Katsunori,Motomatsu, Shinya,Koyama, Koichi,Fukase, Koichi
-
p. 2010 - 2012
(2008/09/19)
-
- Ionic liquid-supported proline as catalyst in direct asymmetric aldol reaction
-
Ionic-liquid-supported proline derivative was synthesized starting from L-proline and was used to catalyze direct asymmetric aldol reaction of acetone with aldehydes. The yield and optical purity of the condensation products, the corresponding β-hydroxy carbonyl compounds were comparable with those obtained under homogeneous conditions. Moreover, the catalyst can be reused for at least four times.
- Chen, Zhuo,Li, Yong,Xie, Hui,Hu, Chang-Gang,Dong, Xian
-
experimental part
p. 1807 - 1810
(2009/09/06)
-
- Proline-catalyzed asymmetric aldol reaction in guanidine-derived ionic liquids
-
A remarkable improvement of both the chemical yield (from 6% to 82%) and the enantiomeric excess (up to >99%), of (S)-proline catalyzed direct aldol reactions of a wide range of aldehydes with acetone was found when hexasubstituted or pentasubstituted guanidinium salts were added as ionic liquids. Effects of temperature, amount of proline and the type of guandidinium salts on the outcome of the reaction were investigated.
- Shah, Jabbar,Blumenthal, Haiko,Yacob, Zekarias,Liebscher, Juergen
-
supporting information; scheme or table
p. 1267 - 1270
(2009/06/17)
-
- Dipeptide-catalyzed direct asymmetric aldol reactions in the presence of water
-
The l-proline-based dipeptide has been discovered and developed as an efficient catalyst for the direct asymmetric aldol reactions of unmodified ketones with various aldehydes including aromatic, aliphatic, heteroaromatic, and unsaturated aldehydes in the presence of water at 0 °C. The resulted methodology and optimal conditions led to the corresponding aldol products with high yields (up to 94%) and good enantioselectivities (up to 97% ee).
- Lei, Meng,Shi, Lanxiang,Li, Gong,Chen, Shilv,Fang, Weihai,Ge, Zemei,Cheng, Tieming,Li, Runtao
-
p. 7892 - 7898
(2008/02/09)
-
- Reconstructed hydrotalcite as a highly active heterogeneous base catalyst for carbon-carbon bond formations in the presence of water
-
The aldol reaction of carbonyl compounds is efficiently catalyzed by reconstructed hydrotalcites, obtained by treating the Mg-Al mixed oxide with water, as solid base catalysts in the presence of water. The catalysis of the reconstructed hydrotalcites is attributable to the surface base sites, created during the organization of the layered structure, with uniformly distributed strength. Furthermore, the reconstructed hydrotalcites provide a unique acid-base bifunctional surface capable of promoting the Knoevenagel and Michael reactions of nitriles with carbonyl compounds.
- Ebitani, Kohki,Motokura, Ken,Mori, Kohsuke,Mizugaki, Tomoo,Kaneda, Kiyotomi
-
p. 5440 - 5447
(2007/10/03)
-
- L-Proline catalysed asymmetric aldol reactions in PEG-400 as recyclable medium and transfer aldol reactions
-
L-Proline-catalysed direct asymmetric aldol reaction of acetone with various aldehydes in PEG-400 is described. Recycling of the catalyst and solvent (PEG) was possible up to ten runs without loss of catalyst activity. l-Proline was also found to be an efficient catalyst for the asymmetric transfer aldol reaction between various aldehydes and diacetone alcohol for the first time. Good yields and enantioselectivities were observed with both methods.
- Chandrasekhar,Reddy, N. Ramakrishna,Sultana, S. Shameem,Narsihmulu,Reddy, K. Venkatram
-
p. 338 - 345
(2007/10/03)
-
- Effect of additives on the proline-catalyzed ketone-aldehyde aldol reactions
-
The effect of bases, acids, and water as additives in proline-catalyzed ketone-aldehyde aldol reactions has been studied. While the reaction appears to be relatively tolerant to small amounts of tertiary amine bases or weak acids, it stops completely with strong acids. The use of water as an additive had a highly beneficial effect on reactions that were conducted with a stoichiometric ratio of ketone to aldehyde, especially with cyclic ketones. This allows the efficient use of more precious ketones such as 4-thianone as donors in the direct enantioselective aldol and facilitates purification.
- Pihko, Petri M.,Laurikainen, Katri M.,Usano, Annina,Nyberg, Annika I.,Kaavi, Jatta A.
-
p. 317 - 328
(2007/10/03)
-
- Asymmetric aldol reactions catalyzed by new spiro diamine derivatives
-
Two new organocatalysts derived from l-proline and a novel chiral spiro diamine bearing a C2 symmetric backbone, were introduced for an asymmetric aldol reaction in moderate to good asymmetric induction in up to 76% ee and high yields.
- Jiang, Man,Zhu, Shou-Fei,Yang, Yun,Gong, Liu-Zhu,Zhou, Xiang-Ge,Zhou, Qi-Lin
-
p. 384 - 387
(2007/10/03)
-
- An unexpected inversion of enantioselectivity in direct asymmetric aldol reactions on a unique L-proline/γ-Al2O3 catalyst
-
L-proline adsorbed on γ-Al2O3 unexpectedly switches the enantioselectivity of the direct asymmetric aldol reaction of acetone with p-nitrobenzaldehyde from 68% ee (R configuration for free L-proline catalyst) with 80% yield to 21% ee (S configuration) with 78% yield. The inversion of enantioselectivity was also observed in the direct asymmetric aldol reactions of acetone with several other aromatic aldehydes catalyzed by the L-proline adsorbed on γ-Al2O3. This inversion phenomenon is found to be general for different types of amino acids adsorbed on γ-Al2O3. The hydroxyl groups on γ-Al2O3 are found to be involved in the inversion induction of enantioselectivity in these direct asymmetric aldol reactions.
- Zhong, Lin,Xiao, Jianliang,Li, Can
-
p. 442 - 445
(2007/10/03)
-
- Chiral diols: A new class of additives for direct aldol reaction catalyzed by L-proline
-
(Chemical Equation Presented) Nine C2 symmetric diols have been examined as additives in the L-proline-catalyzed direct aldol reaction with significant improvement in enantioselectivity, conversion efficiency, and yield. Loading of 1 mol % of (S)-BINOL leads to the desired products in up to 98% ee and 90% yield. A transition state is proposed.
- Zhou, Yan,Shan, Zixing
-
p. 9510 - 9512
(2007/10/03)
-
- 4,4′-Disubstituted L-prolines as highly enantioselective catalysts for direct aldol reactions
-
A new series of 4,4′-disubstituted prolines (1a-h) has been developed and tested as organocatalysts in the direct catalytic asymmetric aldol reaction of several aliphatic ketones with aldehydes. Catalyst 1g affords the best enantioselectivities for this transformation. The reaction was carried out in DMF using a catalyst loading of 10 mol% at -10°C to give the aldol products in up to 97% ee for acetone. In the cases of cyclohexanone and cyclopentanone, the corresponding anti-products were obtained in 94% ee.
- Gu, Liuqun,Yu, Menglong,Wu, Xiaoyu,Zhang, Yazhu,Zhao, Gang
-
p. 2223 - 2228
(2007/10/03)
-
- Au(I)-catalyzed cyclization of tert-butyl carbonates derived from homopropargyl alcohols: A catalytic alternative to cyclic enol carbonates
-
Au(I)-complexes catalyze cyclization of tert-butyl carbonates derived from a variety of homopropargyl alcohols. This procedure offers a catalytic alternative to stoichiometric Lewis acids for the preparation of a range of enol carbonates. Georg Thieme Verlag Stuttgart.
- Kang, Ji-Eun,Shin, Seunghoon
-
p. 717 - 720
(2007/10/03)
-
- A novel strategy for the convergent synthesis of 1,3,5,...-polyols: Enone formation, asymmetric dihydroxylation, reductive cleavage, hydride addition
-
Asymmetric dihydroxylation of α,β-unsaturated ketones provided α,β-dihydroxyketones with up to 100% ee. The Cα-O bond of these intermediates or their bis-TMS ethers, acetonides, phenylborates or orthoformiates was cleaved with SmI2, affording β-hydroxyketones. The latter can be reduced to furnish syn- or anti-configured 1,3-diols of any desired configuration. Georg Thieme Verlag Stuttgart.
- K?rber, Karsten,Risch, Philippe,Brückner, Reinhard
-
p. 2905 - 2910
(2007/10/03)
-
- Increased structural complexity leads to higher activity: Peptides as efficient and versatile catalysts for asymmetric aldol reactions
-
(Chemical Equation Presented) Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure.
- Krattiger, Philipp,Kovasy, Roman,Revell, Jefferson D.,Ivan, Stanislav,Wennemers, Helma
-
p. 1101 - 1103
(2007/10/03)
-
- Processes for preparing beta-hydroxy-ketones and alpha,beta-unsaturated ketones
-
Processes for producing β-hydroxy-ketones and α,β-unsaturated ketones are disclosed which comprise the crossed condensation of an aldehyde with a ketone in the presence of a hydroxide or alkoxide of alkali metal or an alkaline earth metal as catalyst. The products of the process, β-hydroxy-ketones and α,β-unsaturated ketones, are useful for the preparation of many commercially important products in the chemical process industries including solvents, drug intermediates, flavors and fragrances, other specialty chemical intermediates.
- -
-
-
- The zirconium alkoxide-catalyzed aldol-tishchenko reaction of ketone aldols
-
The aldol-Tishchenko reaction of ketone aldols as enol equivalents has been developed as an efficient strategy to furnish differentiated 1,3-anti-diol monoesters in one step. The thermodynamically unstable ketone aldols undergo a facile retro-aldolization to yield a presumed zirconium enolate in situ, which then undergoes the aldol-Tishchenko reaction in typically high yields and with complete 1,3-anti diastereocontrol. Evaluation of a broad range of metal alkoxides as catalysts and optimization of the reaction protocol led to a modified zirconium alkoxide catalyst with attenuated Lewis acidity and dichloromethane as solvent, which resulted in suppression of the undesired acyl migration to a large extent. Various ketone aldols have been prepared and subjected to the general process, giving rise to a broad range of differently substituted 1,3-anti-diol monoesters, which may be hydrolyzed to the corresponding 1,3-anti-diols.
- Schneider, Christoph,Hansch, Markus,Weide, Timo
-
p. 3010 - 3021
(2007/10/03)
-
- Synthesis of new chiral auxiliaries for 6π-azaelectrocyclization: 4- and 7-alkyl substituted cis-1-amino-2-indanols
-
The synthesis of new chiral auxiliaries, 7-alkyl substituted cis-1-amino-2-indanol derivatives, was established by the Diels-Alder reaction of 1-substituted dienes with cyclopentenone followed by the asymmetric epoxidation of the resulting indene derivatives and then the Ritter reaction. These bulky cis-aminoindanol derivatives are very effective as chiral auxiliaries and nitrogen sources in the asymmetric 6π-azaelectrocyclization. The corresponding 4-alkyl derivative was also prepared using a similar method.
- Kobayashi, Toyoharu,Tanaka, Katsunori,Miwa, Junichi,Katsumura, Shigeo
-
p. 185 - 188
(2007/10/03)
-
- Development of highly stereoselective asymmetric 6π- azaelectrocyclization of conformationally flexible linear 1-azatrienes. From determination of multifunctional chiral amines, 7-alkyl cis-1-amino-2-indanols, to application as a new synthetic strategy: Formal synthesis of 20-epiuleine
-
The highly stereoselective asymmetric 6π-azaelectrocyclization was achieved as a general synthetic method based on the reaction between the (E)-3-carbonyl-2,4,6-trienal compounds and the (-)-7-alkyl-cis-l-amino-2-indanol derivatives which are effective chiral amines. The 7-alkyl-substituted 2-indanol moiety of the cyclized products was efficiently removed by the novel manganese dioxide oxidation under remarkably mild conditions, and the method was successfully applied to the formal synthesis of optically active 20-epiuleine.
- Tanaka, Katsunori,Kobayashi, Toyoharu,Mori, Hajime,Katsumura, Shigeo
-
p. 5906 - 5925
(2007/10/03)
-
- Proline-catalyzed ketone-aldehyde aldol reactions are accelerated by water
-
Proline-catalyzed aldol reactions between acetone or 4-thianone and different aldehydes are accelerated by addition of 1-10 equivalents of water to the reaction medium, allowing stoichiometric aldol reactions to proceed at acceptable rates.
- Nyberg, Annika I.,Usano, Annina,Pihko, Petri M.
-
p. 1891 - 1896
(2007/10/03)
-
- Dipeptide-catalyzed direct asymmetric aldol reaction
-
(L)-H-Pro-(L)-Phe-OH (4) were found to be efficient catalysts for direct asymmetric aldol reactions between acetone and various aldehydes. The reaction conditions use a DMSO-NMM-PEMG 5000 system at 0 °C in high yields (62-96%) and enantioselectivities (up to >99% ee).
- Shi, Lan-Xiang,Sun, Qi,Ge, Ze-Mei,Zhu, Yong-Qiang,Cheng, Tie-Ming,Li, Run-Tao
-
p. 2215 - 2217
(2007/10/03)
-
- Synthesis of a new proline-derived organic catalyst and its evaluation for direct aldol reaction
-
Aldol condensation of isobutylaldehyde with acetone catalyzed by amides and amines (1-8) derived from L-proline gave β-hydroxy ketone 17 in 80%ee.
- Tanimori, Shinji,Naka, Toshihito,Kirihata, Mitsunori
-
p. 4043 - 4048
(2007/10/03)
-
- Asymmetric aldol reactions in poly(ethylene glycol) catalyzed by L-proline
-
A rapid L-proline catalyzed direct aldol reaction between various aldehydes and acetone was achieved using PEG as the solvent with comparable enantioselectivities and yields to those obtained in other solvents. Recycling the catalyst and solvent (PEG) was possible 10 times without loss of activity.
- Chandrasekhar,Narsihmulu,Reddy, N. Ramakrishna,Sultana, S. Shameem
-
p. 4581 - 4582
(2007/10/03)
-
- Direct organocatalytic aldol reactions in buffered aqueous media
-
Organocatalytic cross-aldol reactions catalyzed by cyclic secondary amines in aqueous media provide a direct route to a variety of aldols including carbohydrate derivatives and may warrant consideration as a prebiotic route to sugars.
- Cordova, Armando,Notz, Wolfgang,Barbas III, Carlos F.
-
p. 3024 - 3025
(2007/10/03)
-
- Stereoselective radical Aryl migration reactions from sulfur to carbon
-
Stereoselective aryl migration reactions from sulfur in sulfonates and sulfonamides to C-centered radicals are reported. The 1,5-aryl migration from sulfur to differently substituted C-centered radicals could be performed with high yields and selectivities. Functionalized aryl groups could also be transferred by this new method. A model to explain the stereochemical outcome of the reaction is presented and some mechanistic aspects of this reaction are discussed. Aryl migration reactions from sulfur in sulfinates to carbon radicals were less efficient, and the corresponding migrations in aryl sulfoxides were not observed at all. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Bossart, Martin,Faessler, Roger,Schoenberger, Jan,Studer, Armido
-
p. 2742 - 2757
(2007/10/03)
-
- Catalytic compositions and methods for asymmetric aldol reactions
-
Methods and compositions are provided for the direct catalytic asymmetric aldol reaction of aldehydes with donor molecules selected from ketones and nitroalkyl compounds. The reactions employ as catalyst a Group 2A or Group 2B metal complex of a ligand of formula I, as defined further herein.
- -
-
-
- Direct asymmetric aldol reactions of acetone using bimetallic zinc catalysts
-
(Equation presented) The enantioselective aldol reaction using a novel binuclear zinc catalyst of acetone with several aldehydes gave products in good yields (62-89%) with a high level of enantioselectivity (ee = 76-92%).
- Trost, Barry M.,Silcoff, Elliad R.,Ito, Hisanaka
-
p. 2497 - 2500
(2007/10/03)
-
- Contrasting steric effects of the ketones and aldehydes in the reactions of the diisopinocampheyl enolborinates of methyl ketones with aldehydes
-
Treatment of the diisopinocampheylborinates of a representative series of methyl ketones with a representative series of aldehydes, both of differing steric requirements provides aldols whose enantiomeric purifies depend on the steric requirements of both the ketones and the aldehydes. This study has shown that increasing the steric requirements of the R group in the ketones has a pernicious effect on the ee, while increasing the steric requirements of the R group in the aldehydes exerts a beneficial effect on the ee.
- Ramachandran, P. Veeraraghavan,Wei-Chu, Xu,Brown, Herbert C.
-
p. 4911 - 4914
(2007/10/03)
-
- On the diastereoselectivity of cyanide addition to β-hydroxyketones: One-pot synthesis of syn β-hydroxycyanohydrins and anti 2,4-dihydroxyamides
-
The intrinsic stereoselectivity of the cyanide addition to β-hydroxyketones in the presence of 18-crown-6 or ZnI2 is lower than that previously reported. However, the reaction bears a practical value in that syn β-hydroxycyanohydrins and anti 2,4-dihydroxyamides can be diastereoselectively obtained in reasonable yields in a one-pot procedure. The high d.e.'s initially reported were due to the work-up procedure, where the HCl converted much faster the anti β-hydroxycyanohydrin than the syn product into the corresponding amide. This faster conversion is explained in terms of antichimeric assistance of β-hydroxyl group. Details are given as to the configurational assignment of products by 2D NMR and molecular mechanisms.
- Batra, Manohar Singh,Aguilar, Francisco J.,Brunet, Ernesto
-
p. 8169 - 8184
(2007/10/02)
-
- Method for the preparation of unsaturated ketones
-
β-hydroxyketones are prepared by reacting an aldehyde with acetone in the presence of perhydroisoindole or pyrrolidine and water. The resulting β-hydroxyketone is further reacted in the presence of a solvent mixture to produce α-β-unsaturated ketones.
- -
-
-
- C-C ASYMMETRIC BOND FORMATION MEDIATED BY OPTICALLY ACTIVE SULFOXIDES
-
Highly stereoselective C-C bond forming reactions can be performed with a variety of optically active sulfinyl derivatives to afford, after desulfurization, optically active sulfur-free products.
- Cinquini, Mauro
-
-
