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Artykuły w czasopismach na temat "Ether(alkyl allyl)|ent"
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Dutta, Lakshmi Narayan, Banani De, Godhuli Pal i Amarendra Patra. "Feasibility of sigmatropic rearrangement on electron-deficient coumarinyl ketones". Canadian Journal of Chemistry 86, nr 5 (1.05.2008): 401–9. http://dx.doi.org/10.1139/v08-037.
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Different alkyl/aryl 7-hydroxy-8-coumarinyl ketones were converted to 7-O-allyl and 7-O-cyclohexenyl ethers and the study of hitherto unreported sigmatropic rearrangement on 7-O-allyl and 7-O-cyclohex-2'-ene-1'-ylcoumarinyl ketones prepared is accounted herein. The rearrangement yielded alkyl/aryl 6-allyl-7-hydroxy-8-coumarinyl ketones 3 and alkyl/aryl 6-cyclohex-2'-en-1'-yl-7-hydroxy-8-coumarinyl ketones 7 as the major products. Interestingly, unusual selectivity was observed in the case of alkyl 7-O-allylcoumarinyl ketones. Thus alkyl 3-allyl-7-hydroxy-8-coumarinyl ketones 4 and alkyl 8-allyl-7-hydroxy-6-coumarinyl ketones 5 were the outcome from alkyl 7-O-allyl-8-coumarinyl ketones and alkyl 4-methyl-7-O-allyl-8-coumarinyl ketones, respectively, albeit in minor yields.Key words: allyloxycoumarinyl ketones, 7-O-cyclohex-2'-en-1'-ylcoumarinyl ketones, sigmatropic rearrangement, 3-allylcoumarinyl ketones, 8-allylcoumarinyl ketones.
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Toncheva-Moncheva, Natalia, Miroslav Dangalov, Nikolay G. Vassilev i Christo P. Novakov. "Thiol–ene coupling reaction achievement and monitoring by “in situ” UV irradiation NMR spectroscopy". RSC Advances 10, nr 42 (2020): 25214–22. http://dx.doi.org/10.1039/d0ra03902k.
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Grossi, Vincent, Damien Mollex, Arnauld Vinçon-Laugier, Florence Hakil, Muriel Pacton i Cristiana Cravo-Laureau. "Mono- and Dialkyl Glycerol Ether Lipids in Anaerobic Bacteria: Biosynthetic Insights from the Mesophilic Sulfate Reducer Desulfatibacillum alkenivorans PF2803T". Applied and Environmental Microbiology 81, nr 9 (27.02.2015): 3157–68. http://dx.doi.org/10.1128/aem.03794-14.
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ABSTRACTBacterial glycerol ether lipids (alkylglycerols) have received increasing attention during the last decades, notably due to their potential role in cell resistance or adaptation to adverse environmental conditions. Major uncertainties remain, however, regarding the origin, biosynthesis, and modes of formation of these uncommon bacterial lipids. We report here the preponderance of monoalkyl- and dialkylglycerols (1-O-alkyl-, 2-O-alkyl-, and 1,2-O-dialkylglycerols) among the hydrolyzed lipids of the marine mesophilic sulfate-reducing proteobacteriumDesulfatibacillum alkenivoransPF2803Tgrown onn-alkenes (pentadec-1-ene or hexadec-1-ene) as the sole carbon and energy source. Alkylglycerols account for one-third to two-thirds of the total cellular lipids (alkylglycerols plus acylglycerols), depending on the growth substrate, with dialkylglycerols contributing to one-fifth to two-fifths of the total ether lipids. The carbon chain distribution of the lipids ofD. alkenivoransalso depends on that of the substrate, but the chain length and methyl-branching patterns of fatty acids and monoalkyl- and dialkylglycerols are systematically congruent, supporting the idea of a biosynthetic link between the three classes of compounds. Vinyl ethers (1-alken-1′-yl-glycerols, known as plasmalogens) are not detected among the lipids of strain PF2803T. Cultures grown on different (per)deuteratedn-alkene,n-alkanol, andn-fatty acid substrates further demonstrate that saturated alkylglycerols are not formed via the reduction of hypothetic alken-1′-yl intermediates. Our results support an unprecedented biosynthetic pathway to monoalkyl/monoacyl- and dialkylglycerols in anaerobic bacteria and suggest thatn-alkyl compounds present in the environment can serve as the substrates for supplying the building blocks of ether phospholipids of heterotrophic bacteria.
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Liepa, AJ, AJ Liepa, JS Wilkie, JS Wilkie, KN Winzenberg i KN Winzenberg. "Preparation of Some 1-Alkyl-4-[1-(ethoxyimino)butyl]-3-hydroxy-5-oxocyclohex-3-ene-1-carboxylic Acid Ester and Amide Herbicides by Reductive Alkylation of 3,5-Dimethoxybenzoic Acid". Australian Journal of Chemistry 42, nr 8 (1989): 1217. http://dx.doi.org/10.1071/ch9891217.
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Reductive alkylation of 3,5-dimethoxybenzoic acid with haloalkanes afforded the 1-alkyl- 3,5-dimethoxycyclohexa-2,5-diene-1-carboxylic acid derivatives (3a-e) which, upon esterification and hydrolysis, furnished methyl 1-alkyl-3-hydroxy-5-oxocyclohex-3-ene-l-carboxylate derivatives (4f-j). Reaction of (4f-j) with butyric anhydride gave methyl 1-alkyl-4-butyryl- 3-hydroxy-5-oxocyclohex-3-ene-1-carboxylate derivatives (6a-e) which were converted into methyl 1-alkyl-4-[1-( ethoxyimino )butyl]-3-hydroxy-5-oxocyclohex-3-ene-1-carbo xyate derivatives (2a-e). Similarly, the oxime O-ether derivative (2f) was prepared from the amide (41), obtained from reaction of (3b) with N,N′- carbonyldiimidazole and dimethylamine followed by hydrolysis.
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Wright, Andrew D., i Richard D. Bowen. "Investigation of the mechanism of alkyl radical elimination from ionised pentenyl methyl and hexenyl methyl ethers by analysis of the collision-induced dissociation mass spectra of C4H7O+ and C5H9O+ ions". Canadian Journal of Chemistry 71, nr 7 (1.07.1993): 1073–85. http://dx.doi.org/10.1139/v93-143.
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Collision-induced dissociation (CID) mass spectra are reported for C4H7O+ and C5H9O+ ions generated by loss of an alkyl radical from 11 isomers of C5H9OCH3+• and 8 isomers of C6H11OCH3+• produced by ionisation of alkenyl methyl ethers derived from stable alkenols. The oxonium product ions have acyclic structures (CH=CHCH=O+CH3 for C4H7O+; CH2=CH(CH3)C=O+CH3, CH3CH=CHCH=O+CH3, or CH2=(CH3)CCH=O+CH3 in the case of C5H9O+). Elimination of a methyl radical does not always occur by simple α-cleavage. Expulsion of an alkyl substituent attached to a carbon atom at either end of the C=C double bond also takes place readily; this process sometimes competes with or pre-empts α-cleavage, as is shown by 2H-labelling experiments. Plausible mechanisms for this σ′-cleavage are considered. A route involving a 1,2-H shift to the radical centre of a distonic ion, followed by γ-cleavage of the resultant ionised enol ether, is shown to provide the most accurate unifying description of this unusual fragmentation. The mechanistic significance of this interpretation of the σ′-cleavage is discussed by analysing the reverse reaction (addition of an alkyl radical to a methyl cationated enal) in frontier molecular orbital terms. A comparison is made between the mechanisms by which an alkyl radical is lost from ionised alkenyl methyl ethers by σ′-cleavage and the parallel process starting from ionised carboxylic acids or isomeric distonic ions derived from these CnH2n+1CO2H+• species. Both classes of fragmentation are best understood to occur via γ-cleavage of a distonic ion of general structure R1CH2CH•C+(X)OR2 (R1 = alkyl; X = OH, R2 = H; or X = H, R2 = CH3), thus yielding (R′)• and CH2 = CHC+(X)OR2.
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Nilsson, Camilla, Neil Simpson, Michael Malkoch, Mats Johansson i Eva Malmström. "Synthesis and thiol-ene photopolymerization of allyl-ether functionalized dendrimers". Journal of Polymer Science Part A: Polymer Chemistry 46, nr 4 (28.12.2007): 1339–48. http://dx.doi.org/10.1002/pola.22474.
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Yu, Ga-Er, Frank Heatley, Colin Booth i Trevor G. Blease. "Anionic polymerization of propylene oxide: Isomerization of allyl ether to propenyl ether end groups". Journal of Polymer Science Part A: Polymer Chemistry 32, nr 6 (30.04.1994): 1131–35. http://dx.doi.org/10.1002/pola.1994.080320615.
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Yu, Qing Bo, Xian Hua Li, Yu Lun Tao i Guo Jun Cheng. "The Characteristic Research of Two Kinds of Block Polymer". Advanced Materials Research 356-360 (październik 2011): 74–77. http://dx.doi.org/10.4028/www.scientific.net/amr.356-360.74.
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Dual end and single end MacroRAFT agents of polystyrene were obtained respectively by polymerizations of styrene in the presence of benzyl 1H-imidazole-1- carbodithioate (BICDT) and 4,4‘-bis(imidazole-1-carbodithioatemethyl)biphenyl (ICTMP) via the thermal initiation. Then copolymerization of allyl glycidyl ether（AGE） with methyl acrylate（MA） was performed to prepare the functional block copolymers in the presence of PSt maeorRATF agents. The results show that the process has good characteristics of living free radical polymerization. However, the top monomer conversion of triblock copolymers comparing diblock copolymers is lower under the same theory molecular weight and the content of monomer.
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Niemczyk, Edyta M., Alvaro Gomez-Lopez, Jean R. N. Haler, Gilles Frache, Haritz Sardon i Robert Quintana. "Insights on the Atmospheric-Pressure Plasma-Induced Free-Radical Polymerization of Allyl Ether Cyclic Carbonate Liquid Layers". Polymers 13, nr 17 (25.08.2021): 2856. http://dx.doi.org/10.3390/polym13172856.
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Plasma-induced free-radical polymerizations rely on the formation of radical species to initiate polymerization, leading to some extent of monomer fragmentation. In this work, the plasma-induced polymerization of an allyl ether-substituted six-membered cyclic carbonate (A6CC) is demonstrated and emphasizes the retention of the cyclic carbonate moieties. Taking advantage of the low polymerization tendency of allyl monomers, the characterization of the oligomeric species is studied to obtain insights into the effect of plasma exposure on inducing free-radical polymerization. In less than 5 min of plasma exposure, a monomer conversion close to 90% is obtained. The molecular analysis of the oligomers by gel permeation chromatography coupled with high-resolution mass spectrometry (GPC-HRMS) further confirms the high preservation of the cyclic structure and, based on the detected end groups, points to hydrogen abstraction as the main contributor to the initiation and termination of polymer chain growth. These results demonstrate that the elaboration of surfaces functionalized with cyclic carbonates could be readily elaborated by atmospheric-pressure plasmas, for instance, by copolymerization.
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Liu, Michael T. H., Yuri N. Romashin i T. K. Venkatachalam. "Photolysis of 3-chloro-3-aryldiazirines in the presence of amines and allyl alcohol". Canadian Journal of Chemistry 72, nr 9 (1.09.1994): 1961–65. http://dx.doi.org/10.1139/v94-250.
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When photolysis of arylchlorodiazirines is performed in the presence of either alkyl- or allyl-substituted amines, either N-alkyl- or N-allyl-substituted amines result as the sole high-yield (64-93%) products. Photolysis in the presence of phenylallylamine produces a rearranged product in poor yield (11–15%) whereas the reaction of allyl alcohol with arylchlorocarbene gives exclusively diallyl acetals in high yield (70%). The rate constants for these reactions were obtained by laser flash photolysis. Allyl phenyl ether forms a cyclopropanated product when treated with arylchlorocarbene. The different behaviour of these compounds may be attributed to the nucleophilicity at the nitrogen and oxygen centres of these compounds, when the latter are subjected to the substitutions described above. The formation of a cyclopropanated product when allyl phenyl ether is used differs from the reaction of bis (methoxycarbonyl) carbene with allyl ethers, as reported in the literature. The formation of this cyclopropanated product demonstrates the absence of an oxonium ylide intermediate during the reaction.
Rozprawy doktorskie na temat "Ether(alkyl allyl)|ent"
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Touma, Marwan. "Nouvelles reactions d'oligomerisation et de telomerisation selectives catalysees par des complexes cationiques du palladium". Toulouse 3, 1986. http://www.theses.fr/1986TOU30139.
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Figadère, Bruno. "Les composes organomanganeux mixtes : addition 1-2 selective sur des aldehydes ou des cetones portant un groupe fonctionnel, enolisation regioselective de cetones : application en synthese". Paris 6, 1987. http://www.theses.fr/1987PA066371.
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Les reactifs organomanganeux rmnx(x=cl, br, i; r=n-, sec- t-alkyl, alcenyl, aryl, alcynyl) s'additionnent aux aldehydes et cetones fonctionnels pour donner selectivement les alcools correspondant avec d'excellents rendements. Les reactifs rmnz(z=nphme) enolisent les cetones avec une excellente regioselectivite. Les enolates manganeux ainsi prepares sont tres aisement acyles, silyles, alkyles, hydroxyalkyles, avec des rendements de 60% a 90%, a la temperature ambiante
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Alvarez, Gonzalez Eleuterio. "Substitution d'ethers et d'alcools allyliques par differents nucleophiles en presence de complexes de nickel(0) : synthese stereoselective des dienes-1,4 a partir des sulfones dieniques avec le chlorure d'isopropylmagnesium en presence de sels de". Paris 6, 1987. http://www.theses.fr/1987PA066064.
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BECAERT, THIERRY. "Etudes pharmacologiques et electrophysiologiques in vitro et in vivo de o-alkyl ethers et de desoxy s-alkyl thioethers derives du glucose. Mise en evidence de proprietes antagonistes calciques". Amiens, 1990. http://www.theses.fr/1990AMIES022.
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L'etude de la toxicite de molecules tensioactives originales derivees du glucose a ete realisee chez la souris. Certains composes, les o-alkyl-3 et les desoxy-3 s-alkyl 1,2 ; d glucofurannose montrent des proprietes anesthesiques, myorelaxantes et anticonvulsivantes. In vitro, ces composes exercent un effet spasmolytique sur le duodenum de rat, suppriment l'activite cardiaque du cur de rat, et suppriment la contractilite du muscle squelettique (soleus) de souris. Une etude electrophysiologique realisee sur fibres musculaires et sur neurone d'ecrevisse montre que ces composes abolissent les potentiels d'action dependant du calcium et l'influx calcique transmembranaire. Etudies en condition de whole cell clamp sur myotubes de souris, ils bloquent les courants portes par les ions barium a travers les canaux calciques de types t et l
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Ghribi, Abdellaziz. "Utilisation des organocuivreux, associés ou non à un acide de lewis, en synthèse asymétrique et dans la préparation des beta-cétophosphonates". Nancy 1, 1986. http://www.theses.fr/1986NAN10059.
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L'action des organocuprates associés à BF::(3) sur des acétals chiraux constitue une voie très originale de synthèse des alcools secondaires optiquement actifs. Les dianons des acides diethylphono 2 alcoiques réagissent avec les aldéhydes par réaction de wittig-horner et conduisent très stéréosélectivement aux acides alpha éthyléniques trisubstitués. L'action des organocuprates sur les chlorures d'acide diethylphosphono-2 alcanoïques, constitue une voie de synthèse très générale des beta cétiogisogibates alpha substitués
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Pollex, Annett. "Viridiofungins and xeniolide F: target oriented synthesis using different rearrangement reactions of a common substrate class". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1160474365794-44380.
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The present dissertation covers the total synthesis of viridiofungin triesters and studies toward the total synthesis of xeniolide F. In both cases, sigmatropic rearrangements of α-allyloxy substituted α,β-unsaturated esters are employed: for the viridiofungin ester synthesis a [2,3]-Wittig rearrangement and for the xeniolide F synthesis a catalytic asymmetric Claisen rearrangement CAC. For both rearrangement reactions the historical development, main characteristic and important variations are discussed. The viridiofungin triester synthesis represents a convergent and highly flexible route toward these natural products. The [2,3]-Wittig rearrangement allowed the diastereoselective synthesis of the polar head group with two adjacent stereogenic centers. The E-configured double bond was formed by a Julia-Kocienski olefination. During the studies toward the total synthesis of xeniolide F a new, diastereoselective strategy for the generation of allyl vinyl ethers with E-configured vinyl ether double bond was established employing rhodium catalyzed OH-insertion and an E-selective Horner-Wadsworth-Emmons olefination. Under the conditions of the catalytic asymmetric Claisen rearrangement (CAC) this highly substituted allyl vinyl ether rearranged diastero- and enantioselectively to the corresponding a-keto ester. This example clearly illustrates the high potential of the CAC as synthetic tool for natural product synthesisIn der vorliegenden Arbeit wird die Totalsynthese von Tirestern der Viridiofungine A, A2 und A4 sowie die Synthese eines Schlüsselintermediates für die Totalsynthese von Xeniolid F dargestellt. In beiden Fällen wird ausgehend von einem α-allyloxysubstituierten α,β-ungesättigten Ester eine Umlagerungsreaktion als Schlüsselschritt eingesetzt: im Falle der Viridiofunginester eine diastereoselektive [2,3]-Wittig-Umlagerung, bei den Arbeiten zur Totalsynthese von Xeniolid F eine diastero- und enantioselektive, katalytische Claisenumlagerung. Für beide Umlagerungsreaktionen werden ausführlich die theoretischen Hintergründe sowie die historische Entwicklung und wichtige Varianten besprochen. Mit der Viridiofungintriestersynthese wird eine konvergente und bezüglich der lipophilen Seitenkette sehr flexible Syntheseroute vorgestellt. Die [2,3]-Wittig-Umlagerung konnte dabei erfolgreich für die diastereoselektive Synthese der hochsubstituierten, polaren Kopfgruppe der Viridiofunginester mit zwei benachbarten stereogenen Zentren (davon eines quartär) eingesetzt werden. Zur Bildung der E-konfigurierten Doppelbindung wurde die Julia-Kocienskie-Olefinierung ausgenutzt. Bei den Arbeiten zur Totalsynthese von Xeniolid F wurde eine neuartige Strategie zur diastereoselektiven Synthese eines Allylvinylethers mit E-konfigurierter Vinyletherdoppelbindung eingesetzt. Die Horner-Wadsworth-Emmons-Olefinierung (HWE-Olefinierung) generierte dabei E-selektiv die Vinyletherdoppelbindung. Das für die HWE-Olefinierung benötigte Phosphonat wurde durch rhodiumkatalysierte OH-Insertion aus einem Allylalkohol und einem Diazaphosphonoacetat hergestellt. Der hochsubstituierte Allylvinylether wurde unter den Bedingungen der katalytisch asymmetrischen Claisenumlagerung umgesetzt und führte mit exzellenter Diastereo- und Enantioselektivität zum entsprechenden α-Ketoester. Anhand dieses Beispiels konnte das Potential der katalytisch asymmetrischen Claisenumlagerung zum Aufbau von hochfunktionalisierten Bausteinen für die Naturstoffsynthese verdeutlicht werden
Części książek na temat "Ether(alkyl allyl)|ent"
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Carlsson, Ingemar, Adrian Harden, Stefan Lundmark, Ana Manea, Nicola Rehnberg i Lennart Svensson. "Allyl Ethers in the Thiol-ene Reaction". W ACS Symposium Series, 65–75. Washington, DC: American Chemical Society, 2003. http://dx.doi.org/10.1021/bk-2003-0847.ch006.
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Taber, Douglass F. "The Paterson Synthesis of (−)-Leiodermatolide". W Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0096.
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(−)-Leiodermatolide 4, isolated from the lithistid sponge Leiodermatium sp., showed 5.0-nM activity against PANC-1 pancreatic carcinoma cells, and reduced toxicity toward normal cells. Ian Paterson of the University of Cambridge established (Angew. Chem. Int. Ed. 2014, 53, 2692) a synthetic route to 4 based on sp2–sp2 coupling, as exemplified by the combination of 1 with 2 to give 3. Addition of the boron enolate of the enantiomerically-pure benzoate 5 to the iodoaldehyde 6 gave 7, that was silylated, reduced, and deprotected to give 1. Addition of the boron enolate of ent-5 to propanal gave 8. The α-acyloxy ketone of 8 served as a masked acylating agent. The addition of allyl magnesium bromide followed by oxidative cleavage led to the ketone 9. The preparation of 2 was completed by diastereoselective Mukaiyama aldol condensation of 9 with the ketene silyl acetal 10. The intramolecular Heck coupling of 1 with 2 presumably proceeded by way of the organo-Pd intermediate 11. β-Hydride elimination could have given one or more of four possible dienes, but in fact the E,E product 3 dominated, as expected. The allylic H’s are activated for elimination, while the H’s β to the silyl ether are deactivated both electronically and sterically. The third component of 4 was the stannane 17. Applying the same strategy, the addition of ent-5 to the aldehyde 12 gave 13, that was protected and condensed with 14 to deliver, after oxidative cleavage, the alkynyl ketone 15. Conjugate addition of iodide proceeded with good geometric control to give 16, that was protected and stannylated to complete the preparation of 17. The diol 3 was oxidatively cleaved, and the resulting aldehyde was carried on to the iodide 18. This was coupled with the stannane 17 to give the diene 19. A sequence of deprotection, oxidation, and further deprotection yielded a tetraol, that was lactonized with high selectivity to give the 16-membered ring of (−)-leiodermatolide 4.
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Taber, Douglass F. "C–O Ring Construction: The Smith Synthesis of (+)-18-epi-Latrunculol A". W Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0046.
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James A. Bull of Imperial College London showed (Angew. Chem. Int. Ed. 2014, 53, 14230) that the malonate 1 could readily be cyclized to the oxetane 2. Davide Ravelli of the University of Pavia functionalized (Adv. Synth. Catal. 2014, 356, 2781) the α position of the oxetane 3 with 4, leading to 5. Frank Glorius of the Westfälische Wilhelms-Universität Münster hydrogenated (Angew. Chem. Int. Ed. 2014, 53, 8751) the furan 6 to give 7 in high ee. Jia-Rong Chen and Wen-Jing Xiao of Central China Normal University converted (Eur. J. Org. Chem. 2014, 4714) the initial Henry adduct from 8 into the cyclic ether 9. Anil K. Saikia of the Indian Institute of Technology, Guwahati cyclized (J. Org. Chem. 2014, 79, 8592) the ene–yne 10 to the ketone 11. Richard C. D. Brown of the University of Southampton developed (Org. Lett. 2014, 16, 5104) a chiral auxiliary that effectively directed the oxidative cyclization of the diene 12 to 13. The chiral auxiliary could be recovered and reused. K. A. Woerpel of New York University showed (Org. Lett. 2014, 16, 3684) that, depending on the solvent, 15 could be added to 14 to give either 16 or 17. Samuel J. Danishefsky of Columbia University and the Memorial Sloan-Kettering Cancer Center also observed (Chem. Eur. J. 2014, 20, 8731) a marked solvent effect on the diastereoselectivity of the reduction of 18 to 19. Xiaoming Feng of Sichuan University added (Chem. Eur. J. 2014, 20, 14493) the ketone 20 to Danishefsky’s diene 21 to give 22 in high ee. Jhillu Singh Yadav of the Indian Institute of Chemical Technology effected (Tetrahedron Lett. 2014, 55, 3996) intramolecular opening of the oxetane of 23 to give, with clean inversion, the cyclic ether 24. Chun-Yu Ho of the South University of Science and Technology, taking advantage (J. Org. Chem. 2014, 79, 11873) of the superior chelating ability of the allyl ether, selectively cyclized 25 to 26. Xuegong She of Lanzhou University used (Angew. Chem. Int. Ed. 2014, 53, 10789) a gold catalyst to convert 27 into the eight-membered ring ether 28.
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Taber, Douglass F. "The Williams Synthesis of (-)-4-Hydroxydictyolactone". W Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0083.
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(-)-4-Hydroxydictyolactone 3, representative of the cyclononene xenicanes isolated from the Dictyotacae algae, readily isomerizes thermally to the more stable ( Z )- 6,7-isomer. Attempts to directly form this strained ring system appeared to be fraught with difficulty. David R. Williams of Indiana University envisoned (J. Am. Chem. Soc. 2009, 131, 9038) that use of Suzuki coupling might ameliorate some of the strain, since at the point of commitment to bond formation, the Pd center would be included in the forming ring. This analysis led specifically to the trans ether 1, as cyclization of the trans ether appeared likely to be more facile than would cyclization of the alternative cis diastereomer. The first challenge was the assembly of the array the four contiguous alkylated stereogenic centers of 1. To this end, the Z secondary ester 7 was prepared from the acetonide 4 , available from mannitol, and ( R )-(+)-citronellic acid, prepared by oxidation of the commercial aldehyde. Addition of 7 to LDA led to decomposition, but inverse addition of LDA to a mixture of the ester, TMSCl, and Et3 N smoothly delivered the ketene silyl acetal. On warming, Ireland-Claisen rearrangement of the ketene silyl acetal led to the acid 8 with remarkable diastereocontrol. The last alkylated stereogenic center of 1 was installed by reductive cyclization of the formate ester 9. Again, the cyclization proceeded with remarkable diastererocontrol. Although the intramolecular reaction of in situ prepared allyl metals is well precedented, the addition to a formate ester had not previously been reported. Although 11 appears to be ready for the long-awaited Suzuki coupling, in fact the TIPS protecting group substantially slowed hydroboration. The free alcohol/methyl acetal was the best substrate for hydroboration, but the free alcohol entered into other side reactions. After extensive experimentation, a happy medium was found with the methyl acetal/TBS ether 1. Selenylation of the lactone 12 followed by oxidative elimination of the selenide delivered the expected Z alkene. Removal of the silyl protecting group had to precede introduction of the second alkene, as the product 3 deteriorated rapidly on exposure to the alkaline conditions of TBAF cleavage.
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Taber, Douglass F. "The Williams Synthesis of (–)-Khayasin". W Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0101.
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The tetranortriterpenoid (–)-khayasin 3 recently emerged as a potent and selective insecticide against the Coconut leaf beetle Brontispa longissima. In considering a synthetic route to 3, Craig M. Williams of the University of Queensland envisioned (J. Org. Chem. 2012, 77, 8913) the convergent preparation of the allyl vinyl ether 1 and subsequent Claisen rearrangement to the enone 2. To pursue this strategy, the ketone 8 and the allylic alcohol 15 had to be prepared in enantiomerically pure form. To this end, the DIP-Cl-derived enolate of the ketone 7 was added to the aldehyde 6 to give a secondary alcohol, exposure of which to KH led to the enone 8 in high ee. Methyl triflate converted the enone into the enol ether 9. The α-pinene used in the preparation of DIP-Cl was 83% ee. The authors have optimized (Adv. Synth. Catal. 2009, 351, 1148) the Morita-Baylis-Hillman addition of cyclohexenone 10 to formaldehyde to give, after silylation, the enone 11. Methylation followed by DIP-mediated aldol condensation with 13 led to the alcohol 14. Exposure of the derived acetate to lithium diisopropylamide induced cyclization and dehydration. Deprotection completed the preparation (Tetrahedron 2006, 62, 7355) of 15. Fortunately, the enantiomers of 15 could be separated chromatographically. Material having >99% ee was taken onto the next step. Warming of 9 and 15 in the presence of acid delivered the coupled ketone 2 accompanied by the ether 1. Further heating of 1 converted it (Chem. Commun. 2011, 47, 2258) to 2. To form the last ring, the enone 2 was epoxidized to give 16. The reduction of 16 with aluminum amalgam gave preparatively useful amounts of 17. Esterification completed the synthesis of 3. Most total syntheses yield only the target natural product. In this biomimetic project, intermediates 15, 2, and 17 were themselves natural products, and oxidation of 17 delivered an additional natural product, 18. The preparation of 14 and of 8 underscores the importance of the asymmetric transformation of prochiral starting materials, cyclic and acyclic. Although DIP-Cl is used in stoichiometric amounts in both cases, it is not expensive. The preparation of 8, in particular, offers a potentially general approach to high ee-substituted cyclohexenones.
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Taber, Douglass. "The Kozmin Synthesis of Spirofungin A". W Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0089.
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Often, 6,6-spiroketals such as Spirofungin A 3 have a strong anomeric bias. Spirofungin A does not, as the epimer favored by double anomeric stabilization suffers from destabilizing steric interactions. In his synthesis of 3, Sergey A. Kozmin of the University of Chicago took advantage (Angew. Chem. Int. Ed. 2007, 46, 8854) of the normally-destablizing spatial proximity of the two alkyl branches of 3, joining them with a siloxy linker to assure the anomeric preference of the spiroketal. The assembly of 1 showcased the power of asymmetric crotylation, and of Professor Kozmin’s linchpin cyclopropenone ketal cross metathesis. To achieve the syn relative (and absolute) configuration of 6, commercial cis-2-butene was metalated, then condensed with the Brown (+)-MeOB(Ipc)2 auxiliary. The accompanying Supporting Information, accessible via the online HTML version of the journal article, includes a succinct but detailed procedure for carrying out this homologation. For the anti relative (and absolute) configuration of 9, it is more convenient to use the tartrate 8 introduced by Roush. Driven by the release of the ring strain inherent in 10, ring opening cross metathesis with 6 proceeded to give the 1:1 adduct 11 in near quantitative yield. The derived cross-linked silyl ether 12 underwent smooth ring-closing metathesis to the dienone 1. On hydogenation, the now-flexible ring system could fold into the spiro ketal. With the primary and secondary alcohols bridged by the linking silyl ether, only one anomeric form, 2, of the spiro ketal was energetically accessible. A remaining challenge was the stereocontrolled construction of the trisubstituted alkene. To this end, the aldehyde 13 was homologated to the dibromide 14. Pd-mediated coupling of the alkenyl stannane 15 with 14 was selective for the E bromide. The residual Z bromide was then coupled with Zn(CH3)2 to give 16. These steps, and the final steps to complete the construction of spirofungin A 3 , could be carried out without exposure to equilibrating acid, so the carefully established spiro ketal confi guration was maintained.
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Taber, Douglass. "The Kobayashi Synthesis of (-)-Norzoanthamine". W Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0105.
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The Zoanthus alkaloids, exemplified by (-)-norzoanthamine 3a and zoanthamine 3b, show promising activity against osteoporosis. Susumu Kobayashi of the Tokyo University of Science assembled (Angew. Chem. Int. Ed. 2009, 48, 1400; Angew. Chem. Int. Ed. 2009, 48, 1404) the challenging tricyclic core of 3a employing the intramolecular Diels-Alder cyclization of 1 to 2. The cyclopentane of 1 served as useful scaffolding, even though it was cleaved en route to 3a. The cyclohexane ring of 1 has five of its six positions substituted, including three that are alkylated quaternary centers. The starting point for the preparation of 1 was the enantiomerically-pure Hajos-Parrish ketone 4, containing the first of the those quaternary centers. Conjugate addition of MeLi established the second quaternary center. The less stable endo alkyl branch of 1 was installed by conjugate addition to the more reactive α-methylene ketone of the cross-conjugated 5, followed by kinetic quench. Addition of vinyl cuprate across the open face of the enone 7 then established the final quaternary center, setting the stage for the intramolecular Diels-Alder reaction. The silyl enol ether from the cyclization of 1 was not stable, so it was directly oxidized to the enone 2. The keto phosphonate 16 for the last two rings of 3a was prepared from the previously-reported crystalline glutamic acid-derived mesylate 12. Reduction and homologation delivered the ester 14, that was condensed with the phosphonate anion 15 to give 16. The congested cyclopentanone 17, derived from 2, was most efficiently deprotonated with n -BuLi. Exposure of the resulting silyl enol ether to ozone led to the α-hydroxylated product 18. Unexpectedly but happily, oxidative cleavage of 18 delivered, after deprotection and reprotection, the more congested aldehyde 19. This cleavage may be proceeding by tautomerization of 18 to the regioisomeric keto alcohol. The aldehyde 19 was condensed with the keto phosphonate 16, to give, after hydrogenation, the keto lactone 20. A series of oxidation state adjustments then completed the synthesis of (-)-norzoanthamine 3a.
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Taber, Douglass F. "The Fukuyama Synthesis of Gelsemoxonine". W Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0091.
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The compact and highly functionalized Gelsemium alkaloids, exemplified by gelsemine (OHL20060403) and gelsemoxonine 3, offer a substantial challenge. The cytotoxicity of closely related alkaloids adds to the interest in this class. Tohru Fukuyama of the University of Tokyo envisioned (J. Am. Chem. Soc. 2011, 133, 17634) that cyclopropane-accelerated Cope rearrangement of 1 could deliver 2, ready for further functionalization to 3. The starting material for the synthesis was the enantiomerically pure acetate 4, for which a practical synthetic route was developed. Conjugate addition of 5 then proceeded away from the acetoxy group to give, after intramolecular alkylation, the cyclopropane 6. Selective protection of the derived triol 7 led to a monopivalate that was oxidized to the keto aldehyde 8. Condensation with the oxindole 9 followed by silylation then completed the assembly of 1. The trisubstituted alkene of 1 was established as a single geometric isomer. It followed that in the product 2, the oxindole and the bridging ether had the appropriate relative stereochemical arrangement. The product silyl enol ether was deprotected with fluoride to liberate the ketone 2. With 2 in hand, the next challenge was the kinetic installation of the less stable secondary aminated stereogenic center. To this end, the aldehyde 10 was exposed to TMS-CN and DBU. Under the reaction conditions, the alkene of the intermediate β,γ-unsaturated silylated cyanohydrin was brought into conjugation. Kinetic quench with allyl alcohol gave 11 with a 4:1 preference for the desired endo diastereomer 11. Inversion of the carboxyl then led to the protected amine 12. The ketone 12 was formylated under modified Vilsmeier-Haack conditions, first with Bredereck’s reagent 13 and then with oxalyl chloride, leading to the chloro aldehyde 14. The chlorine was removed by selective Pd-catalyzed reduction, and the product aldehyde was exposed to ethyl magnesium bromide followed by IBX to give the ethyl ketone 15. Epoxidation of the α,β-unsaturated ketone proceeded across the expected exo face leading to 16. The deprotected amine then opened the epoxide to establish the aminated quaternary center and complete the synthesis of gelsemoxonine 3.
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Taber, Douglass F. "Diels–Alder Cycloaddition: Fawcettimine (Zhai), Sculponeatin N (Zhai), Elansolid B1 (Kirschning), Frondosin A (Wright), Kingianin H (Parker), Rufescenolide (Snyder)". W Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0078.
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En route to fawcettimine 4, Hongbin Zhai of Lanzhou University found (Org. Lett. 2014, 16, 196) that microwave irradiation improved the efficiency of the cycloaddition of the enone 1 with butadiene 2 to give 3. Takuya Kurahashi and Seijiro Matsubara of Kyoto University developed (Org. Lett. 2014, 16, 2594) a Ru complex that promoted the cycloaddition of butadiene with cyclic enones. In the course of a synthesis of sculponeatin N 7, Professor Zhai employed (Org. Lett. 2014, 16, 216) the silyl diene 5. After intramolecular cycloaddition, protonation of the resulting allyl silane with concomitant alkene migration led to the adduct 6. On the way to elansolid B1 10, Andreas Kirschning of Leibnitz Universität Hannover oxidized (Org. Lett. 2014, 16, 568) the alcohol 8 to the enone, that cyclized to 9. Under the influence of MgBr2, the cyclization proceeded with remarkable diastereocontrol. Dennis L. Wright of the University of Connecticut began (J. Am. Chem. Soc. 2014, 136, 4309) the synthesis of frondosin A 13 by preparing the secondary ether 11 in high ee. Diels–Alder cycloaddition of tetrabromocyclopropene gave, after exposure of the initial adduct to water, the dibromoenone 12. Kathlyn A. Parker of Stony Brook University explored (J. Org. Chem. 2014, 79, 919) the amine radical cation-promoted intermolecular Diels–Alder cycloaddition of the bicyclooctadiene 14. Three readily-separated diastereomeric dimers were observed. The diol 15, the precursor to kingianin H 16, was the major product. Scott A. Synder of Scripps/Florida described (J. Org. Chem. 2014, 79, 88) the interesting oxidative coupling of 17 with 18. The product 19 was readily carried on to rufescenolide 20.
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Taber, Douglass. "Transition Metal-Mediated Ring Construction: The Yu Synthesis of 1-Desoxyhypnophilin". W Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0075.
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Both 1 and 3 are inexpensive prochiral starting materials. Tae-Jong Kim of Kyungpook National University devised (Organomet. 2008, 27, 1026) a chiral Cu catalyst that efficiently converted 1 (other ring sizes worked as well) to the enantiomerically pure ester 2. Alexandre Alexakis of the University of Geneva found (Adv. Synth. Cat. 2008, 350, 1090) a chiral Cu catalyst that mediated the enantioselective coupling of 3 with Grignard reagents such as 4 . The π-allyl Pd complex derived from 6 is also prochiral. Barry M. Trost of Stanford University showed (Angew. Chem. Int. Ed. 2008, 47, 3759) that with appropriate ligand substitution, coupling with the phthalimide 7 proceeded to give 8, readily convertible to (-)-oseltamivir (Tamiflu) 9, in high ee. Jonathan W. Burton of the University of Oxford found (Chem Commun. 2008, 2559) that Mn(OAc)3 -mediated cyclization of 10 delivered the lactone 12 with high diastereocontrol. John Montgomery of the University of Michigan observed (Organic Lett. 2008, 10, 811) that the Ni-catalyzed cyclization of 12 also proceeded with high diastereocontrol. Ken Tanaka of the Tokyo University of Agriculture and Technology combined (Angew. Chem. Int. Ed. 2008, 47, 1312) Rh-catalyzed ene-yne cyclization of 14 with catalytic ortho C-H functionalization, leading to 16 in high ee. Eric N. Jacobsen of Harvard University designed (Angew. Chem. Int. Ed. 2008, 47, 1469) a chiral Cr catalyst for the intramolecular carbonyl ene reaction, that converted 17 to 18 in high ee. Using a stoichiometric prochiral Cr carbene complex 20 and the enantiomerically-pure secondary propargylic ether 19, Willam D. Wulff of Michigan State University prepared (J. Am. Chem. Soc. 2008, 130, 2898) a facially-selective Cr-complexed o -quinone methide intermediate, that cyclized to 21 with high ee. A variety of methods have been put forward for the transition metal-mediated construction of polycarbocyclic systems. One of the more powerful is the enantioselective Rh-catalyzed stitching of the simple substrate 22 into the tricycle 23 devised (J. Am. Chem. Soc. 2008, 130, 3451) by Takanori Shibata of Waseda University. Inter alia, ozonolysis of 23 delivered the cyclopentane 24 containing two all-carbon quaternary centers.