Top PDF Use of pseudoephedrine as a practical chiral auxiliary for asymmetric synthesis

Use of pseudoephedrine as a practical chiral auxiliary for asymmetric synthesis

Use of pseudoephedrine as a practical chiral auxiliary for asymmetric synthesis

For example, in the absence of lithium chlmide, the reaction of n-butyl iodide with the enolate derived from pseudoephedrine propionamide proceeds to the extent of only 32% within 5 h at[r]

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1 Acet­amido 1 (1 naphthyl)­ethyl­ene

1 Acet­amido 1 (1 naphthyl)­ethyl­ene

Enamides were extensively studied for practical use as the prochiral materials for the asymmetric synthesis of chiral amines, which can be used as resolving reagents, chiral auxiliaries and intermediates for the synthesis of many biological active substances (Burk et al., 1996; Noyori et al., 1986; Kitamura et al., 1994; Tschaen et al., 1995; Meth-Cohn et al., 1984; Mpango et al., 1980; Baldwin et al., 1980). Herein, we report the crystal structure of an enamide, 1-

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Morozova, Varvara Alexandrovna
  

(2018):


	Stereoselective preparation of chiral polyfunctional secondary alkyllithiums and alkylcoppers and their application towards natural product synthesis.


Dissertation, LMU München: Fakultät für Chemie und Pharm

Morozova, Varvara Alexandrovna (2018): Stereoselective preparation of chiral polyfunctional secondary alkyllithiums and alkylcoppers and their application towards natural product synthesis. Dissertation, LMU München: Fakultät für Chemie und Pharmazie

auxiliaries due to their availability and relative simplicity to install and to remove. In this type of reactions correlations between used auxiliary and the stereochemical outcome are easier determined than in asymmetric catalysis. The stereoselectivity of the transformations is well predictable and the process usually does not require any special optimization. All these aspects make the use of chiral auxiliaries a very reliable method to construct asymmetric molecules. However, there are few drawbacks of the approach. First of all, the introduction and removal of chiral units have to be quantitative and do not disturb any other functionalities in the substrate. The process requires stoichiometric amount of the asymmetric group, which is a big disadvantage in contrast to chiral catalysis. The auxiliary has to be stable under the reaction conditions. Finally, the substrate must have a certain functional group where the chiral moiety could be installed.
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Progress Toward the Synthesis of Apomorphine: Chiral Auxiliary Mediated Interception of an Intramolecularly Formed N-Acyl Iminium Ion

Progress Toward the Synthesis of Apomorphine: Chiral Auxiliary Mediated Interception of an Intramolecularly Formed N-Acyl Iminium Ion

A chiral auxiliary is a molecule with asymmetric centers used to influence the stereochemical outcome of a reaction. It is covalently bonded to the substrate in much the same way as a protecting group. Rather than being able to take advantage of what Woodward defined as absolute asymmetric synthesis, 5 also what Danishefsky called stereochemical correlation, 6 in which two molecules that already contain a stereocenter(s) are joined resulting in new relative stereochemistry, the chiral auxiliary exerts stereocontrol in another manner. This other approach was called relative asymmetric induction by Bartlett 7 and has been described well by Nicolaou and Sorensen: 8
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A facile approach to tryptophan derivatives for the total synthesis of argyrin analogues

A facile approach to tryptophan derivatives for the total synthesis of argyrin analogues

Current methods employed for the synthesis of enantio- merically pure (S)-Trp analogues rely on either enzymatic or chemical approaches. The enzymatic approach involves a final- step resolution of the racemates using N-acylase enzyme, which affords a mixture of the desired product and the un- processed (R)-N-acetyl-tryptophan. 10 Chemical approaches in the past have exploited various chiral auxiliaries to access enantiomerically pure (S)-Trp analogues. For example, Ma et al. 11 utilize a Schöllkopf chiral auxiliary whilst Buelow et al. 6 employ a DuanPhos ligand. We herein report our progress towards the development of a flexible and operationally simple synthetic route to a raft of (S)-Trp analogues. Our strategy exploits a previously reported asymmetric Strecker synthesis of aliphatic α-aminonitriles that employs chiral auxiliary reagents, such as (S)-α-methylbenzylamine, which in turn delivers ali- phatic (S)-amino acids. 12 The new (S)-Trp analogues were then used for the total chemical synthesis of argyrin A and related analogues. In contrast to previously reported solution-based fragment condensation approaches, 10a,13 we also report for the first time a robust Fmoc/tBu solid-phase peptide synthesis (SPPS) strategy for the stepwise assembly of the octapeptide.
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The Asymmetric Baylis-Hillman reaction: Use of chiral Michael acceptors, electrophiles, catalysts and the Lewis acid mediated isomerization of acetates of Baylis-Hillman adducts into trisubstituted alkenes

The Asymmetric Baylis-Hillman reaction: Use of chiral Michael acceptors, electrophiles, catalysts and the Lewis acid mediated isomerization of acetates of Baylis-Hillman adducts into trisubstituted alkenes

The thesis entitled "The Asymmetric Baylis-Hillman reaction: Use of chiral Michael acceptors, electrophiles, catalysts and the Lewis acid mediated isomerization of acetates of the Baylis- Hillman adducts into trisubstituted alkenes" is divided into three chapters. CHAPTER I: Asymmetric Baylis-Hillman reaction: A Review A general introduction to asymmetric Baylis- Hillman reaction has been presented in this chapter. Various methods available for the asymmetric version of Baylis-Hillman reaction are discussed with literature evidences. The Baylis-Hillman reaction1-6 is a carbon-carbon bond forming reaction between the a-position of activated alkenes and carbon electrophiles under the influence of a suitable catalyst, typically a tertiary amine or phosphine, producing multifunctional molecules (Scheme 1). Although more number of tertiary amines are known, DABCO is the most commonly used catalyst for Baylis- Hillman reaction. These densely functionalised molecules are versatile synthetic intermediates in organic synthesis. There are three synthetic ways by which an asymmetric Baylis-Hillman reaction may be realized: use of (a) chiral Michael acceptor (b) chiral electrophile (c) chiral catalyst. a125_figureNO1.jpg" target="_blank"> Figure a) Asymmetric Baylis-Hillman reaction using chiral Michael acceptors: Although various chiral auxiliaries3 such as menthol, nopal and pantolactone were used for asymmetric Baylis?Hillman reaction, the diastereoselectivities obtained were only low to moderate. Leahy and co-workers developed the most impressive asymmetric version of the Baylis-Hillman reaction using camphor-derived Oppolzer's sultam7 as a chiral auxiliary to obtain products with high to excellent enantiomeric excess. Chen and Yang have disclosed a highly efficient diastereoselective Baylis-Hillman reaction using hydrazide as a chiral auxiliary for the direct preparation of optically active a-methylene-b-hydroxy carbonyl compounds. It is noteworthy that both the diastereomers with high optical purity can be obtained by the appropriate choice of reaction conditions. b) Asymmetric Baylis-Hillman reaction using chiral electrophiles: The use of chiral aldehyde3 such as (S)-O-
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Enantioselective syntheses of (+)-epi-Muricatacin and cis, trans-cyclopropyl containing molecules

Enantioselective syntheses of (+)-epi-Muricatacin and cis, trans-cyclopropyl containing molecules

We have accomplished a concise enantioselective total synthesis of (+)-epi- Muricatacin 1d. A key feature of this protocol is a catalytic asymmetric hydrogenation as the genesis of chirality and a chiral auxiliary mediated intramolecular iodoetherification to ensure a high degree of distereo- and enantiocontrol. The critical starting material 5 was prepared in high efficiency with a substrate/ catalyst molar ratio of 1000:1 using asymmetric hydrogenation. Moreover, the flexibility built into the synthesis to generate a library of analogues will be amenable to large-scale synthesis. We demonstrated that the present methodology employing (S,S)-hydrobenzoin as the chiral source and as the oxygen source would be very useful for the synthesis of (+)- epi-Muricatacin from simple achiral substances. Another merit of the present
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NEWER ROUTE FOR THE SYNTHESIS OF N-PYRAZOLYLCARBOXA- SULFONAMIDES

NEWER ROUTE FOR THE SYNTHESIS OF N-PYRAZOLYLCARBOXA- SULFONAMIDES

Dr. Sharad N. Shelke received his Ph.D. degree in Chemistry in 2007 from Research Centre, Department of Chemistry, RayatShikshanSanstha’s, S.S.G.M. College, Kopargaon, Dist: Ahmednagar (MS), India (Recognized Research Centre, Affiliated to University of Pune), under the supervision of Prof. C. H. Gill. Presently, he is working at S.S.G.M. College, Kopargaon as an Assistant Professor. He has investigated various bioactive hertocycles and green method,which is applicable in organic synthesis.In 2005, he received the “Teacher Fellowship” from UGC.He has completed number of projects received from various funding agencies. His research interests are investigation of bioactive heterocyclic compound and designationof green chemical reactionsand their applications in organic synthesis. He has published over 20, scientific articles, including
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Mg(Clo4)2 as A Recyclable Catalyst for Synthesis of 4H-Chromenes

Mg(Clo4)2 as A Recyclable Catalyst for Synthesis of 4H-Chromenes

We report a novel one pot three component synthesis of functionalized 4H-chromene derivatives in the presence of Mg(ClO 4 ) 2 as catalyst. This reaction series was found to be highly effective under reflux conditions. Mg(ClO 4 ) 2 is an effective catalyst and provides a new and useful method for the synthesis of pyrannulated heterocyclic systems by condensation of arylaldehydes, dimedonand malononitrile. The catalyst is environmentally friendly, inexpensive, clean, safe, nontoxic, and easily obtained. Moreover, the procedure offers several advantages including high yields, clean reaction conditions, and no pollution threat to the environment, which together make a useful and attractive process for synthesis of these compounds.
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Cheemala, Narasimha Murthy
  

(2007):


	Synthesis of New Chiral Phosphine Ligands and Their Applications in Asymmetric Catalysis.


Dissertation, LMU München: Fakultät für Chemie und Pharmazie

Cheemala, Narasimha Murthy (2007): Synthesis of New Chiral Phosphine Ligands and Their Applications in Asymmetric Catalysis. Dissertation, LMU München: Fakultät für Chemie und Pharmazie

Although high enantioselectivities were achieved in the hydrogenation of imines of type 52, the removal of the 3,5-dimethylphenyl group from the amine 53 was difficult. In general, secondary amines with 4-methoxy or 2-methoxyphenyl on the nitrogen atom of the amine can be cleaved under practical conditions to provide chiral primary amines. 100 Since the imines with N-(4-methoxyphenyl) group 50b, 50e, 50g and N-(2-methoxyphenyl) group 50i provided the corresponding amines in moderate enantioselectivities (entries 2; 5, 7, and 9 of Table 10), we searched for another substrate. We thought that N-aryl imine 56a with a 3,5-dimethyl-4- methoxyphenyl group on the imine nitrogen could also be the ideal substrate for the
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Enhanced asymmetric transmission in hyperbolic epsilon near zero slabs

Enhanced asymmetric transmission in hyperbolic epsilon near zero slabs

Abstract. We investigate the asymmetric transmission for forward and backward propagation of tilted circular polarized optical waves in subwavelength epsilon-near- zero hyperbolic slabs. This chiral-optical effect is solely triggered by anisotropy without resorting to any breaking of reciprocity and chiral symmetries or spatial nonlocal effects. Remarkably, we show that the asymmetric transmission undergoes a dramatic enhancement near the epsilon-near-zero condition. This happens since, close to the zero-crossing point, the extraordinary waves can accumulate the desired propagation phase even though the slab is ultrathin and, by varying excitation angles and slab thickness, we engineer this phase thus achieving a huge asymmetric transmission. The proposed strategy holds promise for realizing ultra-compact and efficient polarization devices in different frequency range even at very high frequency (ultraviolet) since the effect is merely due to anisotropy and it is available without resorting to nanofabrication processes.
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Polymers of Platinum Metals Complexes Immobilised on Electrodes60-68

Polymers of Platinum Metals Complexes Immobilised on Electrodes60-68

This preliminary study clearly shows that for asymmetric elec- trocatalytic hydrogenation, effective use can be made of the selectivity of a chiral platinum metal complex, in homoge[r]

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Catalytic enantioselective synthesis of α chiral azaheteroaryl ethylamines by asymmetric protonation

Catalytic enantioselective synthesis of α-chiral azaheteroaryl ethylamines by asymmetric protonation

Here, we present a method for the asymmetric synthesis of this important compound class based on a chiral phosphoric acid (CPA)-catalyzed dearomatizing aza-Michael/rearomatizing asymmetric protonation of 1,1-vinyl azaheterocycles (Scheme 1b). This provides direct modular access to chiral azaheteroarylethyl amines from simple precursors via the formation of a new C-N bond, and with concomitant formation of the α-stereocentre in high enantioselectivity. [6] DFT studies are

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Asymmetric synthesis of chiral arsines from phosphine-stabilised arsenium salts

Asymmetric synthesis of chiral arsines from phosphine-stabilised arsenium salts

V Table of Contents DECLARATION 11 iii ABSTRACT TABLE OF CONTENTS ACKNOWLEDGEMENTS LIST OF ABBREVIATIONS CHAPTER 1: Introduction V vm ix 1 1.1 Chirality 2 1.2 Tertiary Arsines - Configur[r]

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Emergence of single-molecular chirality from achiral reactants

Emergence of single-molecular chirality from achiral reactants

Intrigued by this problem, Frank 8 anticipated in 1953 that an asymmetric reaction from achiral reactants could be possible if the chiral product acts as an asymmetric catalyst for its own production (asymmetric autocatalysis). This concept of self- replication was demonstrated in solution by means of the Soai reaction 9 , which forms the landmark experiment of an asymmetric autocatalytic reaction. Typically, the Soai reaction gives the product in solution in favour of the enantiomer, which at the onset is present in the largest amount. Starting the reaction from achiral conditions results in an amplification in enantiomeric excess (ee) ranging from 15 to 91% (ref. 10), which can be further enhanced if the reaction product is repeatedly isolated and subjected to a new Soai reaction 11 . The necessity of this repetition emphasizes the fact that creating chiral discrimination and amplification under achiral reaction conditions in solution is a considerable challenge.
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Progress Toward the Asymmetric Synthesis of (-)-Gephyrotoxin

Progress Toward the Asymmetric Synthesis of (-)-Gephyrotoxin

to set the C6 stereocenter, I tried to reduce the vinyl dihydropyridone to the cis alcohol, which can also undergo Diels-Alder reactions based on Kuethe’s work. There are conditions for reducing dihydropyridones to the trans alcohol, but at this time there was no method for obtaining the desired cis alcohol This transformation would have to be stereoselective for the cis alcohol, as well as chemoselective for the 1,2-reduction of the enone to a vinyl alcohol, and not the 1,4-reduction to give the saturated ketone. Many reactions conditions were tried and it was thought that I might have to investigate the possibility of chiral reducing reagents.
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Micropatterning of cells reveals chiral morphogenesis

Micropatterning of cells reveals chiral morphogenesis

Left-right asymmetry in development and disease Organisms often adopt consistent left-right (LR) asym- metric positioning and morphology of internal organs, a phenomenon known as handedness or chirality. Th e chirality of biomolecules such as sugar and DNA has been recognized for a long time, but the origins of LR asymmetry in living organisms are not yet well under- stood. In general, the LR patterning is considered to follow four steps: (i) LR symmetry breaking by orienting the LR axis with respect to the anteroposterior and dorso ventral axes [1]; (ii) transferring initial chiral infor- ma tion into LR positions in a multicellular fi eld; (iii)  LR asymmetric expression of signaling molecules; and (iv) asymmetric morphogenesis of visceral organs induced
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Enantioselective synthesis of 6,6 disubstituted pentafulvenes containing a chiral pendant hydroxy group

Enantioselective synthesis of 6,6 disubstituted pentafulvenes containing a chiral pendant hydroxy group

isolated 3 to the reaction conditions also produces no 2, disavowing potential intermediates in the H- shift pathway 7a-b. In addition, pathway C would provide regioisomeric 2’ (Scheme 2) if appropriately substituted (regardless of the sense of asymmetric induction). Only pathway B, in which condensation of cyclopentadiene with the acetyl ketone occurs first, correctly accounts for both the regiochemistry and sense of stereochemistry observed in the reaction. The acidity of the α-methyl fulvene group (pK a

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An Investigation into the asymmetric synthesis of imidazolinones via reaction of chiral alpha-amino acid esters with nitrils

An Investigation into the asymmetric synthesis of imidazolinones via reaction of chiral alpha-amino acid esters with nitrils

Reactions 24-251 Reaction Of L-Phenvlalanine Ethvl Ester Hydrochloride And Benzonitrile In The Presence Of Mercurydll Acetate REACTION 24: Mercuryll acetate L-phenylalanine 1 .59 g, 5.0 [r]

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(−) (P) N,N′ Bis­[(5 bromo 2 hy­droxy­phenyl)­methyl­­idene] 6,6′ di­methyl 1,1′ bi­phenyl 2,2′ dimethan­amine

(−) (P) N,N′ Bis­[(5 bromo 2 hy­droxy­phenyl)­methyl­­idene] 6,6′ di­methyl 1,1′ bi­phenyl 2,2′ dimethan­amine

amine and 5-bromosalicylaldehyde. The structure of (I) was determined in order to con®rm the absolute con®guration of the chiral axis. With this structure in hand, the correlation between the Cotton effect displayed by the CD-spectrum of (I) and those of related biphenyl compounds that we have synthesized could then be used to deduce the absolute con®gurations of these latter compounds (Keller & Rippert, 1999).

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