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Artykuły w czasopismach na temat „Stereoselective reaction”

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Data publikacji: 6 września 2023

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1

Misra, Anup Kumar, Arin Gucchait i Monalisa Kundu. "Synthesis of Pentasaccharide Repeating Unit Corresponding to the Cell Wall O-Polysaccharide of Salmonella enterica O55 Strain Containing a Rare Sugar 3-Acetamido-3-deoxy-d-fucose". Synthesis 53, nr 19 (24.06.2021): 3613–20. http://dx.doi.org/10.1055/s-0037-1610777.

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AbstractA pentasaccharide repeating unit corresponding to the cell wall O-antigen of Salmonella enterica O55 containing a rare sugar, 3-acetamido-3-deoxy-d-fucose has been synthesized as its p-methoxyphenyl glycoside using a sequential stereoselective glycosylation strategy. A suitably functionalized 3-azido-3-deoxy-d-fucose thioglycoside derivative was prepared in very good yield and used in the stereoselective glycosylation reaction. Functionalized monosaccharide intermediates were prepared judiciously and stereoselectively assembled to get the desired pentasaccharide derivative in excellent yield.

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2

Rossi, Sergio, Tiziana Benincori, Laura Maria Raimondi i Maurizio Benaglia. "3,3′-Bithiophene-Based Chiral Bisphosphine Oxides as Organocatalysts in Silicon-Derived Lewis Acid Mediated Reactions". Synlett 31, nr 06 (7.01.2020): 535–46. http://dx.doi.org/10.1055/s-0039-1690777.

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This account summarizes the development of new biheteroaromatic chiral bisphosphine oxides. 3,3′-Bithiophene-based phosphine oxides (BITIOPOs) have been successfully used as organocatalysts to promote Lewis base catalyzed, Lewis acid mediated stereoselective transformations. These highly electron-rich compounds, in combination with trichorosilyl derivatives (allyltrichlorosilane and silicon tetrachloride), generate hypervalent silicon species that act as chiral Lewis acids in highly diastereo- and enantioselective organic reactions. Several relevant examples related to these applications are discussed in detail.1 Introduction2 The BITIOPO Family3 Enantioselective Opening of Epoxides4 Enantioselective Allylation of Aldehydes5 Stereoselective Direct (Double) Aldol-Type Reaction with Ketones6 Stereoselective Direct Aldol-Type Reaction with Ester Derivatives7 Conclusions

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3

Klegraf, Ellen, i Horst Kunz. "Stereoselective Synthesis of 3-Substituted and 3,4-Disubstituted Piperidine und Piperidin-2-one Derivatives". Zeitschrift für Naturforschung B 67, nr 4 (1.04.2012): 389–405. http://dx.doi.org/10.1515/znb-2012-0413.

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The stereoselective synthesis of 3-substituted and 3,4-disubstituted piperidine and piperidin-2-one derivatives was achieved starting from 2-pyridone. After N-galactosylation and subsequent O-silylation, nucleophilic addition of organometallic reagents proceeded with high regio- and stereoselectivity at 4-position. Substituents at position 3 were stereoselectively introduced by reaction of electrophiles with amide enolates of the N-galactosyl-2-piperidones.

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4

Woo, Simon, Masood Parvez i Brian A. Keay. "Regio- and stereoselective ring openings of unsymmetrical oxatricyclo adducts". Canadian Journal of Chemistry 75, nr 6 (1.06.1997): 665–80. http://dx.doi.org/10.1139/v97-081.

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SN2′ ring-opening reactions of a number of substituted 11-oxatricyclo[6.2.1.01,6]undec-9-en-5-ones prepared via the intramolecular Diels–Alder reaction employing a furan diene (IMDAF) are reported. Primary, secondary, and tertiary organolithium reagents were capable of effecting the ring-opening reaction, while methyllithium required activation before any ring opening was observed. Hydride reagents, organocuprates, and Grignard reagents were generally ineffective. The ring-opening reaction was highly regio- and stereoselective for attack at C9syn to the bridging oxygen atom provided that C8 was not substituted. A highly stereoselective nucleophilic addition to the carbonyl group anti to the bridging oxygen was also observed. The high selectivity appears to be due to a combination of steric and electronic effects. Keywords: SN2′ reactions, oxatricyclo adducts, Diels–Alder reaction, ring opening.

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5

Penumati, Nageshwar Rao, i Nagaiah Kommu. "Stereoselective Synthesis of (+)-α-Conhydrine from R-(+)-Glyceraldehyde". Organic Chemistry International 2014 (20.10.2014): 1–7. http://dx.doi.org/10.1155/2014/982716.

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Stereoselective synthesis of (+)-α-Conhydrine was accomplished from protected (R)-(+)-glyceraldehyde, a familiar carbohydrate predecessor. Our synthetic strategy featured the following two key reactions. One is Zn-mediated stereoselective aza-Barbier reaction of imine 6 with allyl bromide to afford chiral homoallylic amine 7, and the other is ring-closing metathesis.

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6

Schultz, Jeremy F., Bing Yang i Nan Jiang. "Direct observation of the geometric isomer selectivity of a reaction controlled via adsorbed bromine". Nanoscale 12, nr 4 (2020): 2726–31. http://dx.doi.org/10.1039/c9nr09857g.

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7

Liu, Yuxiao, Yongming Deng, Peter Y. Zavalij, Renhua Liu i Michael P. Doyle. "An efficient route to highly enantioenriched tetrahydroazulenes and β-tetralones by desymmetrization reactions of δ,δ-diaryldiazoaceto-acetates". Chemical Communications 51, nr 3 (2015): 565–68. http://dx.doi.org/10.1039/c4cc08255a.

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8

Ross, Günther, i Ivar Ugi. "Stereoselective syntheses of α-amino acid and peptide derivatives by the U-4CR of 5-desoxy-5-thio-D-xylopyranosylamine". Canadian Journal of Chemistry 79, nr 12 (1.12.2001): 1934–39. http://dx.doi.org/10.1139/v01-186.

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Since 1961, the synthesis of α-amino acids derivatives by the four-component reaction of isocyanides (U-4CR) as a one-pot reaction has been developed. Only recently it was found that a variety of these α-amino acids compounds can be formed stereoselectively by the U-4CR using 1-amino-5-deoxy-5-thio-2,3,4-tri-O-isobutanoyl-β-D-xylopyranose as the amine component. The stereoselectivity inducing auxiliary 5-desoxy-5-thio-D-xylopyranosyl group of the so-formed products can be replaced selectively by hydrogen.Key words: stereoselective U-4CR, chiral amine component, amino carbohydrate, α-amino acid derivatives.

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9

Cantin, Michel, Yao-Chang Xu i Pierre Deslongchamps. "Stereocontrolled construction of A.B.C.[6.6.6] tricycle via transannular Diels–Alder reaction of 14-membered triene macrocycle". Canadian Journal of Chemistry 68, nr 12 (1.12.1990): 2144–52. http://dx.doi.org/10.1139/v90-329.

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The synthesis of the four acyclic trienes 11a, b and 20a, b is reported. The tandem macrocyclization and stereoselective transannular Diels–Alder reaction of acyclic trienes 11b (trans-trans-cis) and 20b (trans-trans-trans) were observed in the presence of Cs2CO3 at 85 °C to give tricycles 30 (TST) and 32 (CAT) respectively. However, treatment of acyclic trienes 11a (cis-trans-cis) and 20a (cis-trans-trans) under the same conditions yielded the 14-membered macrocycles 21 and 23, which were stereoselectively transformed at 250 °C into tricycles 22 (CST) and 24 (CAT) respectively in excellent yield. Keywords: stereocontrolled synthesis, macrocycle, tricyclic compound, transannular Diels–Alder reaction.

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10

Sugita, Kazuyuki, Motoi Kuwabara, Ami Matsuo, Shogo Kamo i Akinobu Matsuzawa. "Stereoselective Convergent Synthesis of Carbon Skeleton of Cotylenin A Aglycone". Synthesis 53, nr 12 (1.02.2021): 2092–102. http://dx.doi.org/10.1055/s-0040-1706684.

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AbstractIn this paper, the synthesis of the carbon skeleton of cotylenin A aglycone is described. The key reactions, including an intramolecular aldol reaction, an aldol coupling reaction, and a ring-closing metathesis, allow for the effective and stereoselective access to the carbon skeleton of cotylenin A aglycone. The stereochemistry was confirmed by single-crystal X-ray crystallographic analyses of related compounds.

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11

Yang, Yang. "Building polyfunctional piperidines: a stereoselective strategy of a three-component Mannich reaction inspired by biosynthesis and applications in the synthesis of natural alkaloids (+)-241D; (−)-241D; isosolenopsin A and (−)-epimyrtine". RSC Advances 5, nr 24 (2015): 18894–908. http://dx.doi.org/10.1039/c4ra14418j.

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12

Yajima, Tomoko, Eriko Yoshida i Masako Hamano. "Diastereoselective radical addition to γ-alkyl-α-methylene-γ-butyrolactams and the synthesis of a chiral pyroglutamic acid derivative". Beilstein Journal of Organic Chemistry 9 (17.07.2013): 1432–36. http://dx.doi.org/10.3762/bjoc.9.161.

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The cis- and trans-stereoselective radical additions to α-methylene-γ-alkyl- γ-lactams were investigated and the scope and limitation of the reaction were also revealed. This stereoselective radical reaction was used for synthesis of chiral pyroglutamic acid derivatives starting from a commercially available chiral amino acid.

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13

Fischer, Róbert, Ondrej Záborský, Radka Štadániová, Jana Doháňošová i Ján Moncol. "Synthesis of Isoxazolidinyl Epoxides by Oxone Treatment of 2,3-Dihydroisoxazoles in Acetone–Water Solution: A New Stereoselective Approach to Hydroxy-Substituted Isoxazolidines". Synthesis 49, nr 22 (27.09.2017): 4942–54. http://dx.doi.org/10.1055/s-0036-1590924.

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A practical and efficient synthesis of new class of isoxazolidinyl epoxides by direct treatment of 4,5-unsubstituted 2,3-dihydroisoxazoles with Oxone and NaHCO3 in acetone/water solution is described. All epoxidation reactions proceed with excellent anti-selectivity and provide stable products in very good yields. A concept for the development of stereoselective approach to 3,4-trans-hydroxy-substituted isoxazolidines, namely triazole derivatives as important molecules in medicinal chemistry is presented. The synthesis is characterized by highly syn-stereoselective conversion of epoxides to anomeric bromoisoxazolidines, which are found to be powerful reaction intermediates for the coupling reactions with various nucleophiles.

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14

Shindo, M., i K. Yaji. "Scandium-Catalyzed Stereoselective Nazarov Reaction". Synfacts 2009, nr 12 (20.11.2009): 1358. http://dx.doi.org/10.1055/s-0029-1218236.

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15

Riant, O., O. Chuzel, J. Deschamps i C. Chausteur. "Stereoselective Tandem Reductive Aldol Reaction". Synfacts 2007, nr 3 (marzec 2007): 0313. http://dx.doi.org/10.1055/s-2007-968183.

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16

Gangadhar, Pamarthi, Sayini Ramakrishna, Ponneri Venkateswarlu i Pabbaraja Srihari. "Stereoselective total synthesis and structural revision of the diacetylenic diol natural products strongylodiols H and I". Beilstein Journal of Organic Chemistry 14 (4.09.2018): 2313–20. http://dx.doi.org/10.3762/bjoc.14.206.

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The stereoselective total synthesis of strongylodiol H and I has been accomplished. The synthetic procedure comprised the stereoselective reduction of a ketone functionality in an ene–yne–one employing CBS as a catalyst and a Cadiot–Chodkiewicz coupling reaction as the key reaction steps. A common aldehyde intermediate has been used for the synthesis of both strongylodiols.

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17

Janzen, Alexander F., i Meehae Jang. "Isomerization, fluorine exchange, and stereoselective synthesis of cis- and trans-F2TePh3Cl: application of the coordination model of reaction mechanisms". Canadian Journal of Chemistry 67, nr 1 (1.01.1989): 71–75. http://dx.doi.org/10.1139/v89-012.

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The stereoselective synthesis of cis- and trans-F2TePh3Cl (phenyl substituents adopt a mer arrangement) via 5-coordinate cations Ph3TeFCl+ and [Formula: see text] is described. trans-F2TcPh3Cl isomerizes to the thermodynamically more stable cis isomer, and cis -F2TePh3Cl has non-equivalent fluorines which undergo stereoselective fluorine exchange, as confirmed by 19F and l25Te nmr spectroscopy. These results are consistent with an intermolecular mechanism of isomerization and fluorine exchange involving Te—F bond cleavage.The coordination model of reaction mechanisms provides a unified description of stereochemical rearrangements, ligand exchange processes, and chemical reactions in these, and related, octahedral and trigonal bipyramidal compounds. Keywords: synthesis of cis- and trans-F2TcPh3Cl, isomerization of octahedral Te compounds, fluorine exchange in cis-F2TePh3Cl, synthesis of Ph3TeF, coordination model of reaction mechanisms.

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18

Escalante, Carlos H., Eder I. Martínez-Mora, Carlos Espinoza-Hicks, Alejandro A. Camacho-Dávila, Fernando R. Ramos-Morales, Francisco Delgado i Joaquín Tamariz. "Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole". Beilstein Journal of Organic Chemistry 16 (17.06.2020): 1320–34. http://dx.doi.org/10.3762/bjoc.16.113.

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A highly regio-, chemo- and stereoselective divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles is herein described, starting from 2-formylpyrrole and employing Diels–Alder and Heck arylation reactions. 3-(N-Benzyl-2-pyrrolyl)acrylates and 4-(pyrrol-2-yl)butenones underwent a highly endo-Diels–Alder cycloaddition with maleimides to furnish octahydropyrrolo[3,4-e]indoles, which served as precursors in the regioselective synthesis of aza-polycyclic skeletons via an intramolecular Heck arylation reaction. Through the latter reaction, the 3-(N-benzyl-2-pyrrolyl)acrylates give rise to 3-(pyrrolo[2,1-a]isoindol-3-yl)acrylates. A further oxidative aromatization of the polycyclic intermediates provides the corresponding polycyclic pyrrolo-isoindoles and isoindolo-pyrrolo-indoles. A theoretical study on the stereoselective Diels–Alder reactions, carried out by calculating the endo/exo transition states, revealed the assistance of non-covalent interactions in governing the endo stereocontrol.

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19

Pereira, Ana Margarida, Honorina Cidade i Maria Elizabeth Tiritan. "Stereoselective Synthesis of Flavonoids: A Brief Overview". Molecules 28, nr 1 (3.01.2023): 426. http://dx.doi.org/10.3390/molecules28010426.

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Stereoselective synthesis has been emerging as a resourceful tool because it enables the obtaining of compounds with biological interest and high enantiomeric purity. Flavonoids are natural products with several biological activities. Owing to their biological potential and aiming to achieve enantiomerically pure forms, several methodologies of stereoselective synthesis have been implemented. Those approaches encompass stereoselective chalcone epoxidation, Sharpless asymmetric dihydroxylation, Mitsunobu reaction, and the cycloaddition of 1,4-benzoquinone. Chiral auxiliaries, organo-, organometallic, and biocatalysis, as well as the chiral pool approach were also employed with the goal of obtaining chiral bioactive flavonoids with a high enantiomeric ratio. Additionally, the employment of the Diels–Alder reaction based on the stereodivergent reaction on a racemic mixture strategy or using catalyst complexes to synthesise pure enantiomers of flavonoids was reported. Furthermore, biomimetic pathways displayed another approach as illustrated by the asymmetric coupling of 2-hydroxychalcones driven by visible light. Recently, an asymmetric transfer hydrogen-dynamic kinetic resolution was also applied to synthesise (R,R)-cis-alcohols which, in turn, would be used as building blocks for the stereoselective synthesis of flavonoids.

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20

Feng, Xiujuan, Haixia Zhang, Wenbo Lu, Yoshinori Yamamoto, Abdulrahman Almansour, Natarajan Arumugam, Raju Kumar i Ming Bao. "Stereoselective Synthesis of Vinyl Iodides through Copper(I)-Catalyzed Finkelstein-Type Halide-Exchange Reaction". Synthesis 49, nr 12 (11.04.2017): 2727–32. http://dx.doi.org/10.1055/s-0036-1588988.

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An efficient method for the stereoselective synthesis of vinyl iodides is described. The reactions of vinyl bromides with potassium iodide proceed smoothly in the presence of a copper catalyst under mild reaction conditions to produce the corresponding vinyl iodides stereospecifically and in satisfactory to excellent yields.

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21

Smetanin, N. V., S. A. Varenichenko, A. V. Mazepa, O. K. Farat, A. V. Kharchenko i V. I. Markov. "Atom-economic Michael reaction between hydroacridines and arylmaleimides without catalyst/additive". Voprosy Khimii i Khimicheskoi Tekhnologii, nr 5 (październik 2022): 102–9. http://dx.doi.org/10.32434/0321-4095-2022-144-5-102-109.

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Previously unknown spiroderivatives of 3,1-benzoxazines were synthesized by the reaction of anthranilic acid with cyclic ketones. The interaction of 3,1-spirobenzoxazines with Vilsmeier-Haack reagent (POCl3 (PBr3)/DMF), depending on the amount of formulation agent, leads to the formation of hydroacridones or hydroacridines. Under catalyst- and additive-free conditions, N-arylmaleimides, like Michael's acceptors, are added to the hydroacridines in DMSO to form the corresponding adducts. The reaction proceeds stereoselectively with the formation of a mirror pair of diastereomers, if the products have only two chiral centers. In the presence of three chiral centers in the structure of Michael's adducts, the reaction is not stereoselective. The reaction proceeds by the sp3 hybrid carbon atom under non-catalytic conditions due to the imin-enamine tautomerism of chloro(bromo)hydroacridines. The presented reaction can also be considered as an effective atom-economical aza-ene reaction, which fully meets today's requirements for eco-friendly reaction. The synthesized compounds are potential biologically active substances and can also be used as "building-blocks" for organic synthesis.

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22

Darvesh, Sultan, Andrew S. Grant, David I. Magee i Zdenek Valenta. "An approach to the synthesis of bruceantin. The synthesis of a tetracyclic intermediate". Canadian Journal of Chemistry 67, nr 12 (1.12.1989): 2237–40. http://dx.doi.org/10.1139/v89-348.

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An intermediate (20) containing four of the five rings and seven of the ten chiral centers of bruceantin (1) was prepared. In a key reaction, 3-iodo-1-trimethylsilyl-5-hexen-1-yne (9) was found to add chemoselectively and stereoselectively to a dianion. The sequence also includes a selective attack by a sulfinate (17) on the terminal acetylene C-atom of the dianion of a keto acetylene, a concomitant cyclization in which the acetylene acts as an electrophile, and the use of the resulting allyl sulfoxide for the introduction of oxygen functionality by a reductive rearrangement. Keywords: bruceantin, sigmatropic rearrangement, stereoselective alkylation.

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23

Karak, Milandip, Luiz C. A. Barbosa, Jaime A. M. Acosta, Ariel M. Sarotti i John Boukouvalas. "Thermodynamically driven, syn-selective vinylogous aldol reaction of tetronamides". Organic & Biomolecular Chemistry 14, nr 21 (2016): 4897–907. http://dx.doi.org/10.1039/c6ob00895j.

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24

Clark, J. Stephen, i Michael Popadynec. "Stereoselective Synthesis of the I–L Fragment of the Pacific Ciguatoxins". Toxins 12, nr 12 (24.11.2020): 740. http://dx.doi.org/10.3390/toxins12120740.

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The I–L ring system found in all the Pacific ciguatoxins has been prepared from a tricyclic precursor in a highly stereoselective manner. Subtle differences in the reactivity of the enones present in the seven- and eight-membered rings of the tricyclic ether starting material have been exploited to allow selective protection of the enone in the eight-membered ring. Subsequent distereoselective allylation of the seven-membered ring has been accomplished by a palladium-mediated Tsuji-Trost reaction. The K-ring methyl and hydroxyl groups have been installed in a highly stereoselective manner by sequential conjugate reduction and enolate oxidation reactions. Ring L has been constructed by a use of a novel relay ring-closing metathesis reaction to complete the tetracyclic framework, which possesses the functionality necessary for elaboration of rings I and L and the introduction of ring M.

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Tarui, Atsushi, Yukiko Karuo, Kazuyuki Sato, Kentaro Kawai i Masaaki Omote. "Stereoselective Synthesis of Multisubstituted α-fluoro-β-lactams". Current Organic Chemistry 24, nr 18 (18.11.2020): 2169–80. http://dx.doi.org/10.2174/1385272824666200221114707.

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β-Lactams, found in β -lactam antibiotics, are the structurally distorted cyclic compounds being subjected to nucleophilic acyl substitution reaction. α-Fluorination of β -lactams is a simple and expedient approach to control the reactivity of β-lactam ring toward nucleophilic attack, which would hopefully lead to the new design of future antibiotics. From the viewpoint of obtaining multisubstituted α -fluoro-β-lactams, α -bromo-α- fluoro-β-lactams are considered as key compounds for structure functionalization, including nucleophilic substitution reaction, aldol-type reaction and metal-catalyzed crosscoupling reaction. All the reactions can be conducted smoothly to afford a variety of multisubstituted α-fluoro-β-lactams. During the course of the examination, chiral α,α-difluoro- β-lactams and α -bromo-β-fluoro-α-lactams are successfully obtained, which are considered potent precursors for making stereocontrolled multisubstituted α-fluoro-β-lactams.

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Soorukram, Darunee, Manat Pohmakotr, Chutima Kuhakarn i Vichai Reutrakul. "Stereoselective Synthesis of Tetrahydrofuran Lignans". Synthesis 50, nr 24 (2.10.2018): 4746–64. http://dx.doi.org/10.1055/s-0037-1610289.

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This short review aims to summarize the reports on stereoselective synthesis of naturally occurring tetrahydrofuran lignans published during the period of 2006 to 2018. The stereoselective construction of non-natural tetrahydrofuran frameworks is not included in this review.1 Introduction2 Stereoselective Synthesis of 2,5-Diaryltetrahydrofuran (CL5-a)2.1 Synthesis of CL5-a via Friedel–Crafts Arylation or Nucleophilic Addition/Reduction of γ-Butyrolactones2.2 Synthesis of CL5-a via Intramolecular Cyclization of 1,4-Diarylbutanediols2.3 Synthesis of CL5-a via Diastereoselective Hydrogenation of Furan Derivatives2.4 Synthesis of CL5-a via Cycloaddition Reaction of Substituted Cyclopropane Derivatives3 Stereoselective Synthesis of 2-Aryl-4-benzyltetrahydrofuran (CL5-b)4 Stereoselective Synthesis of 3,4-Dibenzyltetrahydrofuran (CL5-c)5 Conclusions

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Singh, Nidhi, i Jaya Pandey. "Advances in Henry Reaction: A Versatile Method in Organic Synthesis". Mini-Reviews in Organic Chemistry 17, nr 3 (28.04.2020): 297–308. http://dx.doi.org/10.2174/1570193x16666190214150144.

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: Henry reaction is an important reaction employing carbonyls which furnishes β-nitro alcohol, nitroalkene, α-nitro ketones, β-amino alcohol as products and byproducts that may be transfigured as building blocks for other synthetic reactions. This paper focuses on various synthetic routes for Henry reaction, a versatile reaction of high significance in organic synthesis. The paper discusses the chemistry and plausible products of the reaction, along with the various available synthetic routes for the same, ranging from classical conventional methods to modern methods of green chemistry trends. Use of various catalysts as rate enhancer as well as use of various catalysts as enantioselective frontman for stereoselective reactions, have been described in this work.

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Gualandi, Andrea, Luca Mengozzi i Pier Cozzi. "Stereoselective SN1-Type Reaction of Enols and Enolates". Synthesis 49, nr 15 (13.06.2017): 3433–43. http://dx.doi.org/10.1055/s-0036-1588871.

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Stereoselective alkylation of enolates represents a valuable and important procedure for accessing carbon–carbon-bond frameworks in natural and nonnatural product synthesis. Usually, activated electrophilic partners that react through an SN2 mechanism are employed. To overcome the limitations due to reduced reactivity and steric hindrance, SN1-type reactions can be considered a valid and practical alternative. Accessible enolates can be used in stereoselective (diastereo- or enantioselective) reactions with electrophilic carbenium ions, either used as stable reagents or generated in situ from suitable precursors. The results achieved in this active field are summarized in this review.1 Introduction2 Alcohols in SN1-Type Reactions with Enolates2.1 Enantioselective Reactions with Metal Complexes2.2 Organocatalytic Enantioselective Reactions3 Alcohols and Alcohol Derivatives in SN1-Type Reactions with Enolates: Enantioselective Reactions with Metal Enolates4 Isolated Carbenium Ions in SN1-Type Reactions with Enolates: Enantioselective Reactions with Metal Enolates5 Miscellaneous6 Conclusion

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Baikadi, Karunakar, Anil Talakokkula i A. Narsaiah. "Stereoselective Total Synthesis of Macrolide Sch-725674 and C-7-epi-Sch-725674". SynOpen 03, nr 01 (styczeń 2019): 26–35. http://dx.doi.org/10.1055/s-0037-1611665.

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The stereoselective total synthesis of Sch-725674 in 14 linear synthetic steps with 10.3% overall yield is described. The synthesis started from commercially available starting materials, d-ribose and (R)-benzyl glycidol. The key reactions involved CBS reduction, Julia–Kocienski olefination, Horner–Wadsworth–Emmons reaction, and Shiina macrolactonization.

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Liu, Yingchun, Ted S. Sorensen i Fang Sun. "Stereoselective 1,3-debromination reactions". Canadian Journal of Chemistry 71, nr 2 (1.02.1993): 258–62. http://dx.doi.org/10.1139/v93-037.

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The metallate, PPN+Cr(CO)4NO−, was used for the 1,3-debrominative reductive cyclization of the (±) and meso isomers of dimethyl 2,4-dibromoglutarate and dimethyl 2,4-dibromo-2,4-dimethylglutarate. In both (±) isomers, the reaction is stereospecific in giving the trans cyclopropane product. In the meso case, the reaction is unselective in the first case, but distinctly favors the cis cyclopropane isomer in the second set of compounds. This (±) and meso pair thus represent the first example of near stereospecificity in the debrominations of both 1,3-dibromo diastereomers. Using an enantiomerically enriched dimethyl 2,4-dibromoglutarate, and determining the absolute stereochemistry of the cyclopropane product, it was found that a strict double inversion [Formula: see text] mechanism is involved in the (±) debromination reaction and presumably also in the near-stereospecific meso case reported above.

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Soto, Martín, Irene Sanz-Machín, Humberto Rodríguez-Solla i Vicente Gotor-Fernández. "Chemoenzymatic Stereoselective Synthesis of trans-Flavan-4-ols via Lipase-Catalyzed Kinetic Resolutions". Catalysts 11, nr 11 (27.10.2021): 1296. http://dx.doi.org/10.3390/catal11111296.

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Flavan-4-ols are a subclass of flavonoids that are present in complex molecules with application in the industrial sector as pigments, antioxidants, or antimitotics, among many others. The most traditional way to achieve their synthesis is from naturally abundant flavanones, asymmetric transfer hydrogenation reactions or bioreduction being well known strategies, while their preparation from racemic flavan-4-ols has been less explored. In this article, we have focused on the synthesis of a series of trans-flavan-4-ols bearing different substitution patterns in the aromatic ring to explore later the potential of lipases as biocatalysts for stereoselective acylation reactions. Therefore, a series of flavanones have been chemically prepared, starting from the corresponding benzaldehydes by aldol condensation with 2′-hydroxyacetophenone in a strongly basic medium, and later transformed into the corresponding racemic trans-flavan-4-ols following a carbonyl reduction, Mitsunobu reaction, and ester deprotection sequence. A screening of lipases and optimization of the reaction conditions for the stereoselective acylation of racemic 2-phenylchroman-4-ol were performed before expanding the best reaction conditions to the kinetic resolution of other 2-arylchroman-4-ols. Interestingly, the combination of AK lipase from Pseudomonas fluorescens as enzyme and vinyl acetate as both acyl donor and solvent allowed the performance of highly asymmetric transformations (E > 200, 50–99% eeS and >99% eeP) under mild reaction conditions (30 °C and 250 rpm).

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Khrimyan, Ashot P., Oganes A. Gharibyan, Ludvík Streinz, Zdeněk Wimmer, Miroslav Romaňuk i Shaliko O. Badanyan. "The hydroalumination-iodination of enyne α-alcohols: Synthesis of 3-methyl-2,4-alkadien-1-ols". Collection of Czechoslovak Chemical Communications 54, nr 12 (1989): 3284–93. http://dx.doi.org/10.1135/cccc19893284.

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It has been found that the reaction course of hydroalumination-iodination using 2-methyl-5-hexen-3yn-2-ol and (6E)-9,13-dimethyl-6,12-tetradecadien-4-yn-3-ol as substrates is ambiguous. The subsequent reaction of lithium dimethyl cuprate with iodo dienols unlike that of iodo alkenols is non-stereoselective. These reactions have been used for the synthesis of a juvenile hormone mimic (4E, 6E)-5,9,13-trimethyl-4,6,12-tetradecatrien-3-ol.

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Marin, Lucile, Soufyan Jerhaoui, Emilie Kolodziej, Régis Guillot, Vincent Gandon, Françoise Colobert, Emmanuelle Schulz, Joanna Wencel‐Delord i David Lebœuf. "Sulfoxide‐Controlled Stereoselective Aza‐Piancatelli Reaction". Advanced Synthesis & Catalysis 363, nr 17 (29.07.2021): 4277–82. http://dx.doi.org/10.1002/adsc.202100848.

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Baba, A., S. Babu, M. Yasuda, Y. Okabe i I. Shibata. "Stereoselective Reformatsky Reaction of Indium Enolates". Synfacts 2006, nr 9 (wrzesień 2006): 0930. http://dx.doi.org/10.1055/s-2006-949268.

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Rama Rao, K., T. N. Srinivasan i N. Bhanumathi. "A stereoselective biocatalytic diels-alder reaction". Tetrahedron Letters 31, nr 41 (styczeń 1990): 5959–60. http://dx.doi.org/10.1016/s0040-4039(00)98004-3.

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Byk, G., i E. Kabha. "A Solid-Supported Stereoselective Multicomponent Reaction". Synfacts 2006, nr 7 (czerwiec 2006): 0739. http://dx.doi.org/10.1055/s-2006-941902.

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Bauer, Adriano, i Nuno Maulide. "A Stereoselective Reductive Hosomi–Sakurai Reaction". Organic Letters 20, nr 5 (22.02.2018): 1461–64. http://dx.doi.org/10.1021/acs.orglett.8b00276.

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Kapa, Prasad, Chen Kau-Ming, Repic Oljan i Hardtmann E. Goetz. "Stereoselective aldol reaction with chiral acetates". Tetrahedron: Asymmetry 1, nr 10 (styczeń 1990): 703–6. http://dx.doi.org/10.1016/s0957-4166(00)82378-2.

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Roy, Tamal, Myungjo J. Kim, Yang Yang, Suyeon Kim, Gyumin Kang, Xinyi Ren, Anders Kadziola, Hee-Yoon Lee, Mu-Hyun Baik i Ji-Woong Lee. "Carbon Dioxide-Catalyzed Stereoselective Cyanation Reaction". ACS Catalysis 9, nr 7 (maj 2019): 6006–11. http://dx.doi.org/10.1021/acscatal.9b01087.

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SANO, Shigeki. "Development of Highly Stereoselective Reactions Utilizing Heteroatoms : New Approach to the Stereoselective Horner-Wadsworth-Emmons Reaction". YAKUGAKU ZASSHI 120, nr 5 (2000): 432–44. http://dx.doi.org/10.1248/yakushi1947.120.5_432.

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Grigg, Ronald, Suren Husinec i Vladimir Savic. "Stereoselective cyclo-addition reactions of azomethine ylides catalysed by in situ generated Ag(I)/bisphosphine complexes". Journal of the Serbian Chemical Society 75, nr 1 (2010): 1–9. http://dx.doi.org/10.2298/jsc1001001g.

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Stereoselective cyclo-addition reactions of azomethine ylides promoted by in situ generated Ag(I)/bisphosphine complexes were studied. Under the optimized conditions, the pyrrolidine products were isolated in up to 84 % yield and with up to 71% e.e. The effects of various reaction variables on the stereoselectivity were also investigated.

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42

Varga, Eszter, László Tamás Mika, Antal Csámpai, Tamás Holczbauer, György Kardos i Tibor Soós. "Mechanistic investigations of a bifunctional squaramide organocatalyst in asymmetric Michael reaction and observation of stereoselective retro-Michael reaction". RSC Advances 5, nr 115 (2015): 95079–86. http://dx.doi.org/10.1039/c5ra19593d.

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The mechanism of cinchona–squaramide organocatalytic Michael addition was studied usingin situIR and NMR experiments. As a result, not only kinetic parameters were determined but a stereoselective retro-Michael reaction was also observed.

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Aitouna, Abdelhak Ouled, Ali Barhoumi i Abdellah Zeroual. "A Mechanism Study and an Investigation of the Reason for the Stereoselectivity in the [4+2] Cycloaddition Reaction between Cyclopentadiene and Gem-substituted Ethylene Electrophiles". Scientiae Radices 2, nr 3 (27.07.2023): 217–28. http://dx.doi.org/10.58332/scirad2023v2i3a01.

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The Molecular Electron Density Theory is applied to the [4+2] cycloaddition reaction between cyclopentadiene and gem-substituted ethylene electrophiles. Calculations are made for reactions, activation energies, and reactivity indices. The results of the experiment are perfectly consistent with activation energies, which unequivocally show that this cyclization’s are is highly stereoselective, in addition, based on ELF examination, the mechanism of these [4+2] cycloadditions occurs in two phases, The mechanisms of these reactions demonstrate that the term "pericyclic reaction" is no more relevant in the 21st century and has been replaced by the term "pseudocyclic".

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Busfield, WK, DI Grice, ID Jenkins i SH Thang. "Reaction of t-Butoxy Radicals With Cyclic Alkenes Studied by the Nitroxide Radical-Trapping Technique". Australian Journal of Chemistry 44, nr 10 (1991): 1407. http://dx.doi.org/10.1071/ch9911407.

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The pattern of reactions occurring between t- butoxy radicals and a number of cyclic alkenes has been investigated by the nitroxide radical-trapping technique. The major reaction pathway is allylic abstraction unless this position is at a bridgehead as in norbornene where the major pathway is radical addition. The technique is sufficiently sensitive to identify minor reaction pathways of non-allylic substitution and radical addition when in the presence of extensive allylic substitution. Some stereoselective effects are also detected.

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Minko, Yury, Morgane Pasco, Helena Chechik i Ilan Marek. "Regio- and stereoselective carbometallation reactions of N-alkynylamides and sulfonamides". Beilstein Journal of Organic Chemistry 9 (13.03.2013): 526–32. http://dx.doi.org/10.3762/bjoc.9.57.

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The carbocupration reactions of heterosubstituted alkynes allow the regio- and stereoselective formation of vinyl organometallic species. N-Alkynylamides (ynamides) are particularly useful substrates for the highly regioselective carbocupration reaction, as they lead to the stereodefined formation of vinylcopper species geminated to the amide moiety. The latter species are involved in numerous synthetically useful transformations leading to valuable building blocks in organic synthesis. Here we describe in full the results of our studies related to the carbometallation reactions of N-alkynylamides.

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46

Singh, Surinderjit, M. PS Ishar, Gajendra Singh i Rajinder Singh. "Efficient, microwave-assisted intramolecular 1,3-dipolar cycloadditions of oximes and N-methylnitrones derived from o-alkenylmethoxy-acetophenones". Canadian Journal of Chemistry 83, nr 3 (1.03.2005): 260–65. http://dx.doi.org/10.1139/v05-049.

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Contrary to literature reports, the o-allyloxy- and crotyloxy-acetophenone-oximes (2a, 2b) are transformed to nitrones, which undergo regio- and stereoselective intramolecular 1,3-dipolar cycloadditions, both on microwave heating under solvent free conditions and refluxing in toluene, to afford novel cycloadducts (5a, 5b); the oxazepine-N-oxide (3a) reported to be formed in 98% yield was obtained only as a minor product (~10%). However, o-cinnamyloxy-acetophenone-oxime (2c) under similar conditions undergoes intramolecular N-alkylation to afford nitrone (3c). The reactions carried out under microwave irradiation are cleaner, require shorter reaction times, and have higher yields. Corresponding intramolecular 1,3-dipolar cycloadditions of N-methylnitrones (B), generated in situ from o-alkenylmethoxy-acetophenones (1a1c) and N-methylhydroxylamine under solvent-free microwave irradiation conditions, are completely regio- and stereoselective, require much shorter reaction times, and afford adducts (4a4c) in higher yields, as compared with their thermal counterparts.Key words: cycloadditions, nitrones, oximes, o-alkenylmethoxy-acetophenones, microwave, isoxazolidines.

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Ghorai, Manas K., Subhomoy Das, Kalpataru Das i Amit Kumar. "Stereoselective synthesis of activated 2-arylazetidines via imino-aldol reaction". Organic & Biomolecular Chemistry 13, nr 34 (2015): 9042–49. http://dx.doi.org/10.1039/c5ob01140j.

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Vereshchagin, Anatoly N., Taigib M. Iliyasov, Kirill A. Karpenko, Radmir N. Akchurin i Mikhail E. Minyaev. "Tetrahydropyridines’ Stereoselective Formation, How Lockdown Assisted in the Identification of the Features of Its Mechanism". Molecules 27, nr 14 (7.07.2022): 4367. http://dx.doi.org/10.3390/molecules27144367.

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The multicomponent reaction of aldehydes, cyano-containing C-H acids, esters of 3-oxocarboxylic acid and ammonium acetate led to unexpected results. The boiling of starting materials in methanol for one to two hours resulted in the formation of polysubstituted 1,4,5,6-tetrahydropyridines with two or three stereogenic centers. During the 2020 lockdown, we obtained key intermediates of this six-step domino reaction. A number of fast and slow reactions occurred during the prolonged stirring of the reaction mass at rt. Sequence: 1. Knoevenagel condensation; 2. Michael addition; 3. Mannich reaction; 4. cyclization—fast reactions and cyclization of the product polysubstituted 2-hydroxypiperidine—was isolated after 40 min stirring at rt. Further monitoring proved the slow dehydration of 2-hydroxypiperidine to obtain 3,4,5,6-tetrahydropyridine after 7 days. Then, four-month isomerization occurred with 1,4,5,6-tetrahydropyridine formation. All reactions were stereoselective. Key intermediates and products structures were verified by X-ray diffraction analysis. Additionally, we specified conditions for the selective intermediates’ preparation.

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Elinson, M. N., A. N. Vereshchagin, R. F. Nasybullin, S. I. Bobrovsky, A. I. Ilovaisky, V. M. Merkulova, I. S. Bushmarinov i M. P. Egorov. "General approach to a spiro indole-3,1′-naphthalene tetracyclic system: stereoselective pseudo four-component reaction of isatins and cyclic ketones with two molecules of malononitrile". RSC Advances 5, nr 62 (2015): 50421–24. http://dx.doi.org/10.1039/c5ra03452c.

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Andreev, Mikhail V., Vladimir A. Potapov, Maxim V. Musalov i Lyudmila I. Larina. "A New Family of Vinyl Selenocyanates with the Amide Function Based on the Reaction of Potassium Selenocyanate with 3-Trimethylsilyl-2-Propynamides". Catalysts 13, nr 9 (30.08.2023): 1257. http://dx.doi.org/10.3390/catal13091257.

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An efficient approach to a novel family of (Z)-3-amino-3-oxo-1-propenyl selenocyanates was developed based on the reaction of KSeCN with 3-trimethylsilyl-2-propynamides in the presence of ammonium chloride in methanol. The reaction was accompanied by a desilylation process. The products were not formed under the same reaction conditions in the absence of ammonium chloride, which was used for the first time in the reactions of selenocyanates with acetylenes. The use of this new methodology allowed the reaction to carry out in a regio- and stereoselective fashion as anti-addition affording vinyl selenocyanates with a (Z)-configuration in high yields.

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