- Desymmetrisation of: Meso -diones promoted by a highly recyclable polymer-supported chiral phosphoric acid catalyst
-
A polystyrene-supported BINOL-derived chiral phosphoric acid has been applied to the desymmetrisation of meso-diones to produce enantioenriched cyclohexenones. The catalytic resin has proven highly active and robust, giving rise to Hajos-Parrish or Wieland-Miescher type products in good yields and enantioselectivities, while allowing for extended recycling.
- Clot-Almenara, Lidia,Rodríguez-Escrich, Carles,Pericàs, Miquel A.
-
p. 6910 - 6914
(2018/02/23)
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- A Highly Active Polymer-Supported Catalyst for Asymmetric Robinson Annulations in Continuous Flow
-
The preparation through Robinson annulation of enantiopure building blocks with both academic and industrial relevance, such as the Wieland-Miescher and Hajos-Parrish ketones, has suffered from important drawbacks, such as the need for high catalyst loading or extremely long reaction times. Here we report a heterogenized organocatalyst based on Luo's diamine for fast and broad-scope enantioselective Robinson annulation reactions. The polystyrene-supported diamine 19a enables the high-yield, highly enantioselective preparation of a wide range of chiral bicyclic enones under mild conditions, with reaction times as short as 60 min (batch) or residence times of 10 min (flow). In contrast with its homogeneous counterpart 19b, the catalytic resin 19a experiences a notable increase in catalytic activity with temperature in 2-MeTHF (a 10-fold decrease in reaction times without erosion in enantioselectivity is observed from room temperature to 55 °C). The scope of the transformation in batch mode has been illustrated with 14 examples, including examples only reported in poorly enantioenriched (22n) or in racemic form (22k). Enantiopure 22k has been used as the starting material for a straightforward formal synthesis of the antibiotic and antifeedant sesquiterpene (-)-isovelleral (24). The heterogenized catalyst 19a admits extended recycling (10 cycles) and has been used to develop the first asymmetric Robinson annulations in continuous flow. The potential of the flow process is illustrated by the large-scale preparation of the Wieland-Miescher ketone (65 mmol in 24 h of operation, TON of 117) and by a sequential flow experiment leading to a library of eight enantioenriched diketone compounds.
- Canellas, Santiago,Ayats, Carles,Henseler, Andrea H.,Pericàs, Miquel A.
-
p. 1383 - 1391
(2017/08/09)
-
- Lipase-catalyzed domino Michael-aldol reaction of 2-methyl-1,3-cycloalkanedione and methyl vinyl ketone for the synthesis of bicyclic compounds
-
Synthesis of bicyclic compounds was achieved via a lipase-catalyzed, stereoselective, domino Michael-aldol reaction of 2-methyl-1,3-cycloalkanedione and methyl vinyl ketone. Appropriate reaction conditions, including the type of enzyme, solvent, and temperature, were determined. In addition, the effects of solvent polarity and addtives were investigated. The reaction proceeded in the presence of lipase AS in a solution of 20% acetone in dimethylsulfoxide (DMSO) at 10 °C for 8 days, followed by the addition of p-toluenesulfonic acid (TsOH) to afford bicyclic compounds in 51-83% yields with moderate stereoselectivity. Although this domino Michael-aldol reaction showed only moderate stereoselectivity, even with the acid-supported enhancement of the reaction, these results represent potential new applications for lipase.
- Sano, Kaoru,Kohari, Yoshihito,Nakano, Hiroto,Seki, Chigusa,Takeshita, Mitsuhiro,Tokiwa, Micho,Hirose, Yoshihiko,Uwai, Koji
-
-
- One-pot synthesis of Wieland-Miescher ketone by enzymes
-
We first report that lipase from porcine pancreas catalyzed Robinson annulation in the organic media to synthesize the Wieland-Miescher ketone. The promiscuous catalytic activity of lipase in the Robinson reaction is due to an important role played by lipase activity in both the Michael addition and Aldol reaction.
- Lai, Yi-Feng,Zhang, Peng-Fei
-
p. 4077 - 4082
(2015/06/30)
-
- Pyrimidine-derived prolinamides as recoverable bifunctional organocatalysts for enantioselective inter- and intramolecular aldol reactions under solvent-free conditions
-
Chiral L-prolinamides 2 containing the (R,R)- and (S,S)-trans-cyclohexane-1,2-diamine scaffold and a 2-pyrimidinyl unit are synthesized and used as general organocatalysts for intermolecular and intramolecular aldol reactions with 1,6-hexanedioic acid as a co-catalyst under solvent-free conditions. The intermolecular reaction between ketone-aldehyde and aldehyde-aldehyde must be performed under wet conditions with catalyst (S,S)-2b at 10 °C, which affords anti-aldols with high regio-, diastereo-, and enantioselectivities. For the Hajos-Parrish-Eder-Sauer-Wiechert reaction, both diastereomers of catalyst 2 give similar results at room temperature in the absence of water to give the corresponding Wieland-Miescher ketone and derivatives. Both types of reactions were scaled up to 1 g, and the organocatalysts were recovered by extractive workup and reused without any appreciable loss in activity. DFT calculations support the stereochemical results of the intermolecular process and the bifunctional role played by the organocatalyst by providing a computational comparison of the H-bonding networks occurring with catalysts 2a and 2b. The intermolecular ketone-aldehyde and aldehyde-aldehyde aldol reactions and the Hajos-Parrish-Eder-Sauer-Wiechert versions with the employment of chiral L-prolinamides containing the (R,R)- and (S,S)-trans-cyclohexane-1,2-diamine scaffold and a 2-pyrimidinyl unit are successfully performed under solvent-free conditions; WMK = Wieland-Miescher ketone.
- Vizcaíno-Milla, Pascuala,Sansano, José M.,Nájera, Carmen,Fiser, Béla,G?mez-Bengoa, Enrique
-
supporting information
p. 2614 - 2621
(2015/04/27)
-
- Novel supported and unsupported prolinamides as organocatalysts for enantioselective cyclization of triketones
-
A novel prolylsulfonamide derived from ethylene diamine and its supported counterpart has been prepared and tested as enantioselective intramolecular aldol reaction of cyclic and acyclic triketones. Good to excellent yields and enantioselectivities have been obtained in water and under solvent free conditions.
- Pedrosa, Rafael,Andrés, José María,Manzano, Rubén,Pérez-López, César
-
supporting information
p. 3101 - 3104
(2013/06/27)
-
- A practical protocol for asymmetric synthesis of wieland-miescher and hajos-parrish ketones catalyzed by a simple chiral primary amine
-
This article describes a simple chiral primary amine catalyzed efficient and practical protocol for the large-scale synthesis of Wieland-Miescher and Hajos-Parrish ketones as well as their analogues. Georg Thieme Verlag Stuttgart. New York.
- Xu, Changming,Zhang, Long,Zhou, Pengxin,Luo, Sanzhong,Cheng, Jin-Pei
-
p. 1939 - 1945
(2013/07/26)
-
- Recoverable silica-gel supported binam-prolinamides as organocatalysts for the enantioselective solvent-free intra- and intermolecular aldol reaction
-
Silica-gel supported binam-derived prolinamides are efficient organocatalysts for the direct intramolecular and intermolecular aldol reaction under solvent-free conditions using conventional magnetic stirring. These organocatalysts in combination with benzoic acid showed similar results to those obtained under similar homogeneous reaction conditions using an organocatalyst of related structure. For the intermolecular process, the aldol products were obtained at room temperature and using only 2 equiv of the ketone with high yields, regio-, diastereo- and enantioselectivities. Under these reaction conditions, also the cross aldol reaction between aldehydes is possible. The recovered catalyst can be reused up to nine times providing similar results. More interestingly, these heterogeneous organocatalysts can be used in the intramolecular aldol reaction allowing the synthesis of the Wieland-Miescher and ketone analogues with up to 92% ee, with its reused being possible up to five times without detrimental on the obtained results.
- Ba?ón-Caballero, Abraham,Guillena, Gabriela,Nájera, Carmen,Faggi, Enrico,Sebastián, Rosa María,Vallribera, Adelina
-
p. 1307 - 1315
(2013/02/23)
-
- Asymmetric synthesis of Wieland-Miescher and Hajos-Parrish ketones catalyzed by an amino-acid-derived chiral primary amine
-
This paper describes a simple chiral primary amine-catalyzed highly efficient and practical protocol for the synthesis of both Wieland-Miescher ketone and Hajos-Parrish ketone as well as their analogues. The reaction can be conducted in gram scale with 1%
- Zhou, Pengxin,Zhang, Long,Luo, Sanzhong,Cheng, Jin-Pei
-
experimental part
p. 2526 - 2530
(2012/05/05)
-
- Proline imidazolidinones and enamines in Hajos-Wiechert and Wieland-Miescher ketone synthesis
-
Readily available aromatic prolinamides obtained from the acid chloride of proline hydrochloride and anilines induce large enantiomeric excesses in intramolecular aldol condensations. Imidazolidinones derived from the reaction of the catalyst and enamines
- de Arriba, ángel L. Fuentes,Simón, Luis,Raposo, César,Alcázar, Victoria,Morán, Joaquín R.
-
scheme or table
p. 4841 - 4845
(2009/10/02)
-
- STEROID ANALOGUES FOR NEUROPROTECTION
-
Provided are steroid analogues functionalized with polar substituents at the C3 and/or C20 positions of the steroid ring system that exhibit improved water solubility. Also provided are pharmaceutical compositions comprising the steroid analogues and methods using the novel steroid analogues for the treatment and prevention of neurodegeneration in a patient following injury to the central nervous system.
- -
-
Page/Page column 130
(2009/10/21)
-
- Water versus solvent-free conditions for the enantioselective inter- and intramolecular aldol reaction employing l-prolinamides and l-prolinethioamides as organocatalysts
-
Organocatalysts 1, derived from L-proline and (1S,2R)-cis-l-aminoindan-2-ol or (R)-l-aminoin-dane, are evaluated as promoters in the direct asymmetric aldol reaction between ketones and aromatic aldehydes in the presence of water and under solvent-free reaction conditions. L-Prolinethioamides 1c and 1d exhibited higher enantioselectivity than the corresponding prolinamides 1a and 1b in the model aldol reaction between cyclohexanone and 4-nitro-benzaldehyde in the presence of 4-nitrobenzoic acid as cocatalyst. In particular, L-prolinethioamide 1d (5 mol%), derived from L-proline and (R)-1-amino-indane, is shown as the most efficient organocatalyst studied promoting the direct aldol reaction of cyclo-alkyl, alkyl, and a-functionalized ketones with aromatic aldehydes in the presence of water and under solvent-free reaction conditions employing only 2 equivalents of nucleophile. Generally, anft-aldol products are obtained in high yields and excellent diastereo- and enantioselectivities (up to > 98/2 until syn, up to 98% ee). Solvent-free conditions give slightly higher dr and ee than using water as solvent. In addition, organocatalyst Id can be easily recovered by extractive work-up and reused. Prolinethio-amide Id (5 mol%) in combination with 4-NO2C6H4CO2H (5 mol%) is also a very effective or-ganocatalytic system for the asymmetric solvent-free intramolecular Haj os-Parrish-Eder-Sauer-Wiechert reaction with comparable or higher levels of enantioselectivity (up to 88% ee) to other reported catalysts in organic solvents.
- Almasi, Diana,Alonso, Diego A.,Balaguer, Andrea-Nekane,Najera, Carmen
-
supporting information; scheme or table
p. 1123 - 1131
(2009/12/07)
-
- Chiral phosphoric acid catalyzed desymmetrization of meso-1,3diones: Asymmetric synthesis of chiral cyclohexenones
-
Chiral effectiveness: The title transformation is applicable to a wide variety of substrates to give chiral cyclohexenones in high yields and with excellent enantioselecti vity (see scheme). To clarity the origin of the enantioselectivity ONIOM calculations were carried out
- Mori, Keiji,Katoh, Takuya,Suzuki, Tohru,Noji, Takuya,Yamanaka, Masahiro,Akiyama, Takahiko
-
supporting information; experimental part
p. 9652 - 9654
(2010/04/28)
-
- Structural constraints for C2-symmetric heterocyclic organocatalysts in asymmetric aldol reactions
-
Asymmetric aldol reactions were studied in the presence of heterocyclic bimorpholine- and bipiperidine-type organocatalysts. Bimorpholine derivatives were found to be more reactive and more selective in intramolecular, as well as intermolecular, reactions.
- Laars, Marju,Kriis, Kadri,Kailas, Tiiu,Mueuerisepp, Aleksander-Mati,Pehk, Tonis,Kanger, Tonis,Lopp, Margus
-
p. 641 - 645
(2008/09/20)
-
- Combining multi-catalysis and multi-component systems for the development of one-pot asymmetric reactions: Stereoselective synthesis of highly functionalized bicyclo[4.4.0]decane-1,6-diones
-
We have developed a direct amine/acid-catalyzed stereoselective hydrogenation of a variety of Wieland-Miescher (W-M) ketones, Hajos-Parrish (H-P) ketones and their analogs with organic hydrides (Hantzsch esters) as the hydrogen source. This astonishingly simple and biomimetic approach was used to construct highly functionalized chiral bicyclo[4.4.0]decane-1,6-diones 6 in a diastereoselective fashion. This is an example of the development of a new technology by the combination of multiple catalysts and components in one pot to deliver highly functionalized chiral molecules. The Royal Society of Chemistry 2008.
- Ramachary, Dhevalapally B.,Sakthidevi, Rajasekar
-
supporting information; experimental part
p. 2488 - 2492
(2009/02/02)
-
- N-Tosyl-(Sa)-binam-L-prolinamide as highly efficient bifunctional organocatalyst for the general enantioselective solvent-free aldol reaction
-
N-Tosyl-(Sa)-binam-L-prolinamide (5 mol%) and benzoic acid (1 mol%) were used as catalysts in the enantioselective direct aldol reaction between different ketones and aldehydes under solvent-free conditions in the presence or absence of water. Under these reaction conditions it was possible to reduce the amount of required ketone to two equivalents to give the corresponding aldol products with high yields, regio-, diastereo- and enantioselectivities. The aldol reaction between aldehydes or the intramolecular aldol reaction can be also performed with excellent results. Georg Thieme Verlag Stuttgart.
- Guillena, Gabriela,Nájera, Carmen,Viózquez, Santiago F.
-
scheme or table
p. 3031 - 3035
(2009/10/16)
-
- Short α/β-peptides as catalysts for intra- and intermolecular aldol reactions
-
(Chemical Equation Presented) Short α/β-peptides, containing conformationally restricted cis-β-aminocyclopropylcarboxylic acid units as turn-inducing elements, have been found to be efficient catalysts for inter-and intramolecular aldol reactions. The tripeptide H-(L)-Pro--(L)-Pro-OH was identified to perform especially well in homogeneous and heterogeneous aqueous solutions as well as in organic solvents.
- D'Elia, Valerio,Zwicknagl, Hans,Reiser, Oliver
-
p. 3262 - 3265
(2008/09/19)
-
- Prolinamides versus prolinethioamides as recyclable catalysts in the enantioselective solvent-free inter- and intramolecular aldol reactions
-
A solvent-free asymmetric and direct anti-aldol reaction of aliphatic ketones with aromatic aldehydes catalyzed by recyclable L-prolineamides and L-prolinethioamides 3 is studied. The L-prolinethioamide 3d (5 mol%), derived from L-Pro and (R)-1-aminoindane, is the most efficient catalyst for this process affording the anti-aldol adducts in high yields with excellent diastereo-and enantioselectivities (up to >98/2 dr, up to 98% ee) at 0°C or room temperature. Prolinethioamide 3d is an effective organocatalyst for the first asymmetric, solvent-free, intramolecular Hajos-Parrish-Eder-Sauer-Wiechert reaction with comparable or higher levels of enantioselectivity (up to 88% ee) to reported catalysts in organic solvents. Moreover, organocatalyst 3d can be easily recovered and reused by a simple acid/base extraction.
- Almasi, Diana,Alonso, Diego A.,Najera, Carmen
-
supporting information; experimental part
p. 2467 - 2472
(2009/08/14)
-
- Evaluating β-amino acids as enantioselective organocatalysts of the Hajos-Parrish-Eder-Sauer-Wiechert reaction
-
A systematic study of the effect of substitution within the β-amino acid framework indicates that both β2- and β3- amino acids catalyse the Hajos-Parrish-Eder-Sauer-Wiechert reaction with poor to reasonable levels of enantioselectivity. These results led to the evaluation of the conformationally constrained β-amino acid (1R,2S)-cispentacin, which catalyses the Hajos-Parrish-Eder-Sauer-Wiechert reaction with comparable or higher levels of enantioselectivity to l-proline. The Royal Society of Chemistry.
- Davies, Stephen G.,Russell, Angela J.,Sheppard, Ruth L.,Smith, Andrew D.,Thomson, James E.
-
p. 3190 - 3200
(2008/03/14)
-
- Benzimidazole-pyrrolidine/H+ (BIP/H+), a highly reactive organocatalyst for asymmetric processes
-
A new chiral benzimidazole-pyrrolidine has been devised, which exhibits excellent activities in aminocatalyzed aldol reactions, leading to aldol products in high yields and enantioselectivities in the presence of an equimolar amount of a Broensted acid. This organocatalyst has demonstrated remarkable reactivities in aldol processes even with equimolar amounts of aldehyde and ketone in THF. A discussion of the role of the Broensted acid as a co-catalyst is provided along with some applications of this new class of organocatalyst in Robinson annelation and α-amination processes. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Lacoste, Eric,Vaique, Emilie,Berlande, Muriel,Pianet, Isabelle,Vincent, Jean-Marc,Landais, Yannick
-
p. 167 - 177
(2007/10/03)
-
- Synthesis and use of 3,3′-bimorpholine derivatives in asymmetric Michael addition and intramolecular aldol reaction
-
The synthesis of 3,3′-bimorpholine and its N-alkyl derivatives is described. These new diamine derivatives were revealed to be efficient organocatalysts for the asymmetric Michael addition of aldehydes to nitroalkenes with excellent enantioselectivity (up to 90% ee). The potential of these organocatalysts was also demonstrated for the highly enantioselective intramolecular aldol reaction affording the Wieland-Miescher ketone with tremendous enantioselectivity (up to 95% ee). Georg Thieme Verlag Stuttgart.
- Sulzer-Mosse, Sarah,Laars, Marju,Kriis, Kadri,Kanger, Tonis,Alexakis, Alexandre
-
p. 1729 - 1732
(2008/02/08)
-
- β-Homoamino acids as catalysts in enantioselective intra- and intermolecular aldol reactions
-
β3-Homoamino acids catalyze the intra- (cf. the Hajos-Parrish-Eder-Sauer-Wiechert reaction) as well as the intermolecular aldol reaction. The stereochemical outcome with selectivities of up to 83% ee is reversed in the intramolecular reaction,
- Limbach, Michael
-
p. 3843 - 3847
(2007/10/03)
-
- Enantioselective synthesis of Wieland-Miescher ketone through bimorpholine-catalyzed organocatalytic aldol condensation
-
Novel bimorpholine-derived organocatalysts have been used for highly enantioselective intramolecular aldol reaction affording Wieland-Miescher ketone in high yield and enantioselectivity (up to 92% and 95%, respectively). Georg Thieme Verlag Stuttgart.
- Kriis, Kadri,Kanger, T?nis,Laars, Marju,Kailas, Tiiu,Müürisepp, Aleksander-Mati,Pehk, T?nis,Lopp, Margus
-
p. 1699 - 1702
(2008/02/03)
-
- Highly enantioselective organocatalysis of the Hajos-Parrish-Eder-Sauer- Wiechert reaction by the β-amino acid cispentacin
-
The β-amino acid cispentacin promotes the Hajos-Parrish-Eder-Sauer- Wiechert reaction with levels of enantioselectivity comparable to or higher than proline. The Royal Society of Chemistry 2005.
- Davies, Stephen G.,Sheppard, Ruth L.,Smith, Andrew D.,Thomson, James E.
-
p. 3802 - 3804
(2007/10/03)
-
- Enantiomerically Pure Octahydronaphthalenone and Octahydroindenone: Elaboration of the Substrate Overcame the Specificity of Yeast-Mediated Reduction
-
Substrate specificity on the reduction of bicyclic diketones with a yeast strain, Torulaspora delbrueckii IFO10921, was investigated. Although this yeast efficiently reduces the isolated carbonyl group involved in the (S)-enantiomer of Wieland-Miescher ke
- Fuhshuku, Ken-Ichi,Tomita, Mina,Sugai, Takeshi
-
p. 766 - 774
(2007/10/03)
-
- Solid-supported Robinson annulation under microwave irradiation.
-
Robinson annulation on alumina occurred efficiently on heating with microwave irradiation.
- Takatori, Kazuhiko,Nakayama, Masayasu,Futaishi, Naoko,Yamada, Saori,Hirayama, Shinobu,Kajiwara, Masahiro
-
p. 455 - 457
(2007/10/03)
-
- Kinetic and stereochemical evidence for the involvement of only one proline molecule in the transition states of proline-catalyzed intra- and intermolecular aldol reactions
-
Contrary to the widely accepted mechanism of the Hajos-Parrish-Eder-Sauer-Wiechert reaction, we have obtained evidence for the involvement of only one proline molecule in the transition states of both inter- and intramolecular aldol reactions. Our conclusions are based on kinetic measurements and the absence of nonlinear and dilution effects on the asymmetric catalysis, and are supported by B3LYP/6-31G* calculations. Complementary to recent theoretical studies, our results provide the foundation of a unified enamine catalysis mechanism of proline-catalyzed inter- and intramolecular aldol reactions. Copyright
- Hoang, Lihn,Bahmanyar,Houk,List, Benjamin
-
-
- Inotropic activity of hydroindene amidinohydrazones
-
Several hydroindenic derivatives (7a-methyl-2,3,5,6,7,7a-hexahydro-1H-indenes), bearing an amidinohydrazone at C-5 and different moieties at C-1, have been synthesized and evaluated for their inotropic and chronotropic effects on right- and left-guinea-pig-atria activity. Three of them showed the same profile as digoxin, although with lower potency. The effect on Na+,K+ ATPase (NKA) was also evaluated for these three compounds, observing that two of them, with the same absolute configuration as natural cardenolides, are also NKA inhibitors, while the compound with the opposite configuration lacks such an effect. More interestingly, both active compounds act without affecting the cardiac rhythm. This could be related to the selective inhibition of the human α2β1 isozyme (associated with the inotropic effect) with respect to the α1β1 isozyme (associated with the maintenance of basal ionic levels in the cell and the toxic effect of cardenolides).
- Sevillano,Melero,Caballero,Tomé,Lelièvre,Geering,Crambert,Carrón,Medarde,San Feliciano
-
p. 127 - 136
(2007/10/03)
-
- Asymmetric one-pot Robinson annulations
-
One-pot syntheses of ketol SS-5a, enone S-2 and optically active spiroenediones S-14, R-7 and S-15 are reported.
- Rajagopal,Narayanan,Swaminathan
-
p. 4887 - 4890
(2007/10/03)
-
- Toward the total synthesis of variecolin
-
(matrix presented) An annulative approach toward the total synthesis of the sesterterpenoid variecolin (1) is presented. Synthesis of the key hemiketal, containing the core ABC ring skeleton, has been achieved on a model system by an expeditious route uti
- Molander, Gary A.,Quirmbach, Michael S.,Silva Jr., Luiz F.,Spencer, Keith C.,Balsells, Jaume
-
p. 2257 - 2260
(2007/10/03)
-
- Efficient kinetic resolution of (±)-4-methyl-Hajos-Parrish ketone by baker's yeast reduction
-
Kinetic resolution of (±)-4-methyl-Hajos-Parrish ketone (±)-2a using baker's yeast reduction was investigated. The reaction rate and enantiomeric purity depended on the concentration of substrate and yeast. Under concentrated conditions, (-)-2a and the alcohol (+)-3 were obtained in high enantiomeric excess. Copyright (C) 2000 Elsevier Science Ltd.
- Hioki, Hideaki,Hashimoto, Takefumi,Kodama, Mitsuaki
-
p. 829 - 834
(2007/10/03)
-
- Asymmetric Michael addition of malonate anions to prochiral acceptors catalyzed by L-proline rubidium salt
-
L-Proline rubidium salt catalyzes the asymmetric Michael addition of malonate anions to prochiral enones and enals. This method can be applied to a wide range of substrates to give adducts with a predictable absolute configuration: (S)-adducts from (E)-enones/enals and (R)-adducts from cyclic (Z)-enones. Both the secondary amine moiety and the carboxylate moiety are critical for the catalytic activity and asymmetric induction. Varying the countercation also affects the reaction course. High enantiomeric excesses were attained when di(tert-butyl) malonate was added to (E)-enones in the presence of CsF. The stereochemistry of the Michael reaction indicates that asymmetric induction takes place via enantioface discrimination involving the acceptor α-carbon atom rather than the β-carbon atom.
- Yamaguchi, Masahiko,Shiraishi, Tai,Hirama, Masahiro
-
p. 3520 - 3530
(2007/10/03)
-
- Asymmetric synthesis without solvent
-
Asymmetric syntheses of the diketones S-1, S-6, and S-10 from the precursors 3, 5 and 8 respectively have been carried out in the abscence of solvent employing S-proline as chiral auxiliary.
- Rajagopal, Desikan,Rajagopalan,Swaminathan
-
p. 2189 - 2190
(2007/10/03)
-
- Additive and Medium Effects on Lewis Acid-Promoted Cationic ?-Cyclizations of Alkenyl- and Alkynylcyclopentane-1,3-diones
-
The effects of nucleophilic additives and Bronsted acids, and solvents on BF3*Et2O-promoted cationic ?-cyclizations of alkynyl- and alkenylcyclopentane-1,3-diones are reported.The rates and selectivities of alkynyl dione cyclizations were significantly ef
- Balog, Aaron,Geib, Steven J.,Curran, Dennis, P.
-
p. 345 - 352
(2007/10/02)
-
- Synthesis of Optically Active trans-Cyclononenes. A Possible Approach to Xenicanes
-
Two optically active substituted trans-cyclononenes (13a, 13b) were synthesized from the (-)-Hajos-Parrish diketone.This procedure provides a possible approach for the total synthesis of xenicanes, biologically active compounds isolated from marine organi
- Liu, Gui,Smith, Tim. C.,Pfander, Hanspeter
-
p. 4979 - 4982
(2007/10/02)
-
- Ring-Enlarging Annulatons. A One-Step Conversion of Cyclic Silyl Acyloins and ω-Alkynyl Acetals to Polycyclic Enediones
-
A new sequence of cationic reactions that converts cyclic silyl acyloins and ω-alkynyl acetals to polycyclic enediones is reported.For example, treatment of bis-1,2-((trimethylsilyl)oxy)cyclobutene and 2-(ethylenedioxy)-5-heptyne with excess boron trifluoride etherate in methylene chloride for 2 days provides 4-acetyl-3,5,6,6a-tetrahydro-6a-methyl-1-(2H)-pentalenone in 58percent yield.This product is formed via a sequence involving a Mukaiyama aldol reaction, a pinacol ring expansion, and a 5-exo-dig alkynyl ketone cyclization.In the case of terminal alkynes, the last cyclization occurs in a 6-endo-dig fashion.The scope and limitations of this process are studied, and a number of bi- and tricyclic ring systems are formed.
- Balog, Aaron,Curran, Dennis P.
-
p. 337 - 344
(2007/10/02)
-
- Synthesis of ent-Cholesterol, the Unnatural Enantiomer
-
Cholesterol is ubiquitious in mammals and plays an important role in human health.The unique relationship between enantiomers make ent-cholesterol, the unnatural enantiomer of cholesterol, a valuable new probe of cholesterol function in biochemical systems.We report the first enantioselective total synthesis of ent-cholesterol.
- Rychnovsky, Scott D.,Mickus, Daniel E.
-
p. 2732 - 2736
(2007/10/02)
-
- Dependence of the Lewis Acid-induced Reaction of β-stannyl Ketones upon Substitution Pattern. 1,2-Alkyl Migration versus Cyclopropanation
-
3-Stannylcyclohexanones fully substituted at 2 and 3 positions undergo a 1,2-alkyl migration and cyclopropanation.The balance of the reaction pattern depends upon the steric environment and migratory aptitude of the alkyl groups.
- Fujiwara, Jun,Yamamoto, Taro,Sato, Tadashi
-
p. 1775 - 1778
(2007/10/02)
-
- Annulative Ring Expansions. Direct Conversion of ω-Alkynyl Acetals to Polycyclic Unsaturated Ketones
-
Geminal acylation of ω-acetylenic acetals and bis(silyloxy)cycloalkenes under Lewis acid conditions preceded cationic cyclization of the alkyne onto the ketone to produce polycyclic unsaturated ketones.
- Sisko, Joseph,Balog, Aaron,Curran, Dennis P.
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p. 4341 - 4342
(2007/10/02)
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- The Course of Cyclic Ethylene Acetal Formation from 7a-Methyl-2,3,7,7a-tetrahydro-1H-indene-1,5(6H)-dione
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All attemps to convert the dione (1a) into the 5-monoacetal (8) by direct ethylene acetal formation under mild conditions have led to complex mixtures usually containing the required monoacetal (8), its conjugated enone isomer (9), the diacetal (5) and the 1-monoacetal (2).The diacetal (5) readily forms a dimer (4) in the presence of anhydrous acid, but in dioxan containing aqueous sulfuric acid it is hydrolysed to the 5-monoacetal (8), isolated in 68percent yield after chromatographic separation from the dione (1a).For preparative purposes the most convenient and reliable method for the preparation of (8) is conversion of (1a) into the 1-cyanohydrin (34), formation of the corresponding 5-acetal (36), and elimination of HCN from the 1-cyanohydrin group with pyridine; this gave the 5-monoacetal (8) in 66percent overall yield.
- Brown, Roger F. C.,Burge, Geoffrey L.,Collins, David J.
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p. 117 - 134
(2007/10/02)
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- Asymmetric synthesis of organic compounds
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Optically active organic compounds are prepared starting from optically inactive reactants by means of an optically active agent which influences the course of the reaction. In particular optically active compounds having a "meso" type carbon atom undergo an intramolecular ring closure in the presence of an optically active agent to yield an optically active product having one additional ring. The present process is particularly useful in the preparation of optically active bicyclic diketones which are important intermediates in the total synthesis of steroids.
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