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Formal Total Synthesis (formal + total_synthesis)
Selected AbstractsA Formal Total Synthesis of (±)-1,13-HerbertenediolEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2004Adusuhilli Srikrishna Abstract A formal total synthesis of (±)-1,13-herbertenediol, employing a ring-closing metathesis reaction of the 4-arylhepta-1,6-diene-4-carboxylate 15 as the key reaction, is described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Remarkable Electronic Effect on the Diastereoselectivity of the Heck Reaction of Methyl Cinnamate with Arenediazonium Salts: Formal Total Synthesis of (±)-Indatraline and (±)-SertralineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Julio Cezar Pastre Abstract An efficient and stereoselective protocol for the preparation of ,,,-disubstituted acrylates in good to high yields by means of a Heck,Matsuda arylation was accomplished. The method employs a base- and ligand-free Heck arylation reaction of methyl cinnamate using both electron-deficient and electron-rich arenediazonium salts as electrophiles. The Heck reaction displays a remarkable electronic dependence regarding the diastereoselectivity of the arylation process, which correlates with the electronic nature of the arenediazonium salts employed. A rationale for the observed diastereoselectivity is presented. The overall methodology provides a convenient route to 3-arylindanones and 4-aryltetralones allowing the concise formal total syntheses of the therapeutically important psychoactive compounds (±)-indatraline and (±)-sertraline. [source] Asymmetric Synthesis of Allylsilanes by the Borylation of Lithiated Carbamates: Formal Total Synthesis of (,)-Decarestrictine,D,ANGEWANDTE CHEMIE, Issue 25 2010Michael Binanzer Dipl.-Chem. Enantiokomplementäre Routen zu ,-Hydroxyallylsilanen stehen durch die Reaktion von lithiierten Carbamaten mit ,-Silylvinylboranen offen. Nach der Komplexierung mit (,)-Spartein reagieren die lithiierten Carbamate unter Inversion der Konfiguration, ohne das Diamin dagegen unter Retention (siehe Schema). Diese Methode wurde in einer kurzen formalen Totalsynthese von (,)-Decarestrictin,D angewendet. [source] Rhodium-Catalyzed Asymmetric Enyne Cycloisomerization of Terminal Alkynes and Formal Total Synthesis of (,)-Platensimycin,ANGEWANDTE CHEMIE, Issue 34 2009C. Nicolaou Prof. Effizient und direkt: Die Titelreaktion wird vorgestellt und für eine formale Totalsynthese von (,)-Platensimycin genutzt (siehe Schema; Ts=para -Toluolsulfonyl, binap=2,2,-Bis(diphenylphosphanyl)-1,1,-binaphthalin). [source] The Stereoselective Synthesis of ,-Substituted ,-Amino Secondary Alcohols Based on the Proline-Mediated, Asymmetric, Three-Component Mannich Reaction and Its Application to the Formal Total Synthesis of Nikkomycins B and Bx.CHEMINFORM, Issue 12 2006Yujiro Hayashi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A Formal Total Synthesis of (-)-Limaspermine.CHEMINFORM, Issue 20 2004Yu-ichi Fukuda No abstract is available for this article. [source] ChemInform Abstract: Ring Expansion: Formal Total Synthesis of (-)-Paroxetine.CHEMINFORM, Issue 5 2002Janine Cossy Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A Novel and Highly Stereoselective Intramolecular Formal [3 + 3] Cycloaddition Reaction of Vinylogous Amides Tethered with ,,,-Unsaturated Aldehydes: A Formal Total Synthesis of (+)-Gephyrotoxin.CHEMINFORM, Issue 33 2001Lin-Li Wei Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Intramolecular Alkynylogous Mukaiyama Aldol Reaction Starting from Bicyclic Alkanones Tethered to Alkynyl Esters: Formal Total Synthesis of (±)-Hamigeran,BCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2009Laurence Miesch Dr. Abstract Selecting the ring: tert -Butyldimethylsilyltriflate (TBSOTf)/NEt3 treatment of alkynyl esters tethered to bicycloalkanones leads to the formation of tricyclic allenoates with total diasteroselectivity at the ring junction. An intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt3 dual activation is involved. This novel methodology was illustrated by a formal total synthesis of (±)-hamigeran,B. tert -Butyldimethylsilyltriflate (TBSOTf)/NEt3 treatment of alkynyl esters tethered to bicycloalkanones led to tricyclic allenoates with total diastereoselectivity for the ring junction. The allenoates result from an intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt3 dual activation, with key intermediates of silylalkynylketene acetals. This novel methodology was illustrated by a formal total synthesis of (±)-hamigeran,B. [source] A Formal Total Synthesis of Eleutherobin Using the Ring-Closing Metathesis (RCM) Reaction of a Densely Functionalized Diene as the Key Step: Investigation of the Unusual Kinetically Controlled RCM StereochemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2006Damiano Castoldi Dr. Abstract Asymmetric oxyallylation reactions and ring-closing metathesis have been used to synthesize compound 3, a key advanced intermediate used in the total synthesis of eleutherobin reported by Danishefsky and co-workers. The aldehyde 6, which is readily prepared from commercially available R -(,)-carvone in six steps in 30,% overall yield on multigram quantities, was converted into the diene 5 utilizing two stereoselective titanium-mediated Hafner,Duthaler oxyallylation reactions. The reactions gave the desired products (8 and 12) in high yields (73 and 83,%, respectively) as single diastereoisomers, with the allylic alcohol already protected as the p -methoxyphenyl (PMP) ether, which previous work has demonstrated actually aids ring-closing metathesis compared to other protective groups and the corresponding free alcohol. Cyclization under forcing conditions, using Grubbs' second-generation catalyst 13, gave the ten-membered carbocycle (E)- 14 in 64,% yield. This result is in sharp contrast to similar, but less functionalized, dienes, which have all undergone cyclization to give the Z stereoisomers exclusively. A detailed investigation of this unusual cyclization stereochemistry by computational methods has shown that the E isomer of the ten-membered carbocycle is indeed less thermodynamically stable than the corresponding Z isomer. In fact, the selectivity is believed to be due to the dense functionality around the ruthenacyclobutane intermediate that favors the trans -ruthenacycle, which ultimately leads to the less stable E isomer of the ten-membered carbocycle under kinetic control. During the final synthetic manipulations the double bond of enedione (E)- 16 isomerized to the more thermodynamically stable enedione (Z)- 4, giving access to the advanced key-intermediate 3, which was spectroscopically and analytically identical to the data reported by Danishefsky and co-workers, and thereby completing the formal synthesis of eleutherobin. [source] Remarkable Electronic Effect on the Diastereoselectivity of the Heck Reaction of Methyl Cinnamate with Arenediazonium Salts: Formal Total Synthesis of (±)-Indatraline and (±)-SertralineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Julio Cezar Pastre Abstract An efficient and stereoselective protocol for the preparation of ,,,-disubstituted acrylates in good to high yields by means of a Heck,Matsuda arylation was accomplished. The method employs a base- and ligand-free Heck arylation reaction of methyl cinnamate using both electron-deficient and electron-rich arenediazonium salts as electrophiles. The Heck reaction displays a remarkable electronic dependence regarding the diastereoselectivity of the arylation process, which correlates with the electronic nature of the arenediazonium salts employed. A rationale for the observed diastereoselectivity is presented. The overall methodology provides a convenient route to 3-arylindanones and 4-aryltetralones allowing the concise formal total syntheses of the therapeutically important psychoactive compounds (±)-indatraline and (±)-sertraline. [source] Platinum- and Gold-Catalyzed Rearrangement Reactions of Propargyl Acetates: Total Syntheses of (,)-,-Cubebene, (,)-Cubebol, Sesquicarene and Related TerpenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2006Alois Fürstner Prof. Abstract Propargyl acetates, in the presence of catalytic amounts of late transition-metal salts such as PtCl2 or AuCl3, represent synthetic equivalents of ,-diazoketones. This notion is corroborated by a concise approach to various sesquiterpene natural products starting from readily available substrates. Specifically, (+)-carvomenthone (17) is converted into propargyl acetate (S)- 26 by a sequence involving Stille cross-coupling of its kinetic enol triflate 18, regioselective hydroboration/oxidation of the resulting 1,3-diene 19, and addition of an alkynyl cerium reagent to aldehyde 21 thus obtained. Since the latter step was found to be unselective, the configuration of the reacting propargyl acetate was unambiguously set by oxidation followed by diastereoselective transfer hydrogenation by using Noyori's catalyst 25. Compound (S)- 26, on treatment with PtCl2 in toluene, converted exclusively to the tricyclic enol acetate 27, which was saponified to give norcubebone 11 in excellent overall yield. The conversion of this compound into the sesquiterpene alcohol (,)-cubebol (6) was best achieved with MeCeCl2 as the nucleophile, whereas the formation of the parent hydrocarbon (,)-,-cubebene (4) was effected in excellent yield by recourse to iron-catalyzed cross coupling methodology developed in this laboratory. Since norketone 11 has previously been transformed into (,)-,-cubebene (5) as well as (,)-4-epicubebol 8, our approach constitutes formal total syntheses of these additional natural products as well. Along similar lines, the readily available propargyl acetates 1, 33 and 47 were shown to give access to 2-carene 44, sesquicarene 39, and episesquicarene 51 in excellent overall yields. In this series, however, the cycloisomerization reaction was best achieved with catalytic amounts of AuCl3 in 1,2-dichloroethane as the solvent. In addition to these preparative results, our data provide some insight into the mechanism of these remarkable skeletal rearrangement reactions. Transformations of this type are likely triggered by initial coordination of the alkyne unit of the substrate to the carbophilic transition-metal cation. Formal attack of the alkene moiety onto the resulting ,-complex engenders the formation of an electrophilic cyclopropyl carbene species which subsequently reacts with the adjacent acetate unit to give the final product. The alternative phasing of events, implying initial attack of the acetate (rather than the alkene moiety) onto the metal,alkyne complex, is inconsistent with the stereochemical data obtained during this total synthesis campaign. [source] A Formal Total Synthesis of (±)-1,13-HerbertenediolEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2004Adusuhilli Srikrishna Abstract A formal total synthesis of (±)-1,13-herbertenediol, employing a ring-closing metathesis reaction of the 4-arylhepta-1,6-diene-4-carboxylate 15 as the key reaction, is described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Domino Aza-Claisen/Mannich Cyclization Reaction from a Chiral ,-Alkoxy Enamine or Sequential Alkylation of an ,-Alkoxy Ester Enolate or Nitrile Anion, Followed by an Intramolecular Wittig Reaction: Two (3+2) Annulation Routes to Homochiral 4-Alkyl-4-hydroxy-2-cyclopentenone SynthesisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2003Cyrille Kuhn Abstract A study on the enantioselective synthesis of 4-alkyl-4-hydroxyalkylidene-cyclopentenone prostaglandins is reported. Two (3+2) annulation processes allow the synthesis of homochiral 4-alkyl-4-hydroxy-2-cyclopentenones 4,5, 10,11, and 17. The first process involves a domino aza-Claisen/Mannich cyclization reaction, resulting from the alkylation of an ,-alkoxy-enamine, derived from chiral ,-alkoxy aldehydes 1, 9, or 16 with 3-iodo-2-(methoxymethoxy)prop-1-ene (3) as the acetonyl equivalent. The second process is based on the sequential alkylation of esters 21, 39, or nitrile 20 with acetonyl equivalents 3 or 25, followed by an intramolecular Wittig reaction. As an application, the synthesis of the naturally occurring alkylidene-cyclopentenone prostaglandin clavulone II from the spiro[cyclopentene-furan]one 5 and the formal total synthesis of (+/-)-untenone 19 has been carried out. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Formal Synthesis of the Anti-Angiogenic Polyketide (,)-Borrelidin under Asymmetric Catalytic ControlCHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2010Ashoka V. R. Madduri Abstract Borrelidin (1) is a polyketide that possesses extremely potent anti-angiogenesis activity. This paper describes its formal total synthesis by the most efficient route to date. This modular approach takes optimal benefit of asymmetric catalysis and permits the synthesis of analogues; in addition, the high yields and selectivities obtained eliminate the need for separation of stereoisomers. The upper half of borrelidin has been accessed by iterative copper-catalysed asymmetric conjugate addition of methylmagnesium bromide, whereas synthesis of the lower half of the molecule was achieved by relying on asymmetric hydrogenation and cross-methathesis as key steps. [source] Intramolecular Alkynylogous Mukaiyama Aldol Reaction Starting from Bicyclic Alkanones Tethered to Alkynyl Esters: Formal Total Synthesis of (±)-Hamigeran,BCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2009Laurence Miesch Dr. Abstract Selecting the ring: tert -Butyldimethylsilyltriflate (TBSOTf)/NEt3 treatment of alkynyl esters tethered to bicycloalkanones leads to the formation of tricyclic allenoates with total diasteroselectivity at the ring junction. An intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt3 dual activation is involved. This novel methodology was illustrated by a formal total synthesis of (±)-hamigeran,B. tert -Butyldimethylsilyltriflate (TBSOTf)/NEt3 treatment of alkynyl esters tethered to bicycloalkanones led to tricyclic allenoates with total diastereoselectivity for the ring junction. The allenoates result from an intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt3 dual activation, with key intermediates of silylalkynylketene acetals. This novel methodology was illustrated by a formal total synthesis of (±)-hamigeran,B. [source] | ||||||||||||||||||||||