- Iterative synthesis of alkenes by insertion of lithiated epoxides into boronic esters
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The insertion of lithiated epoxides into boronic esters followed by thermal syn-elimination provides a stereospecific entry to alkenes. This process avoids transition metals and is amenable to iteration to provide higher substitution patterns.
- Bojaryn, Kevin,Fritsch, Stefan,Hirschhaüser, Christoph
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supporting information
p. 2218 - 2222
(2019/04/10)
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- Synthesis of Highly Stereodefined Tetrasubstituted Acyclic All-Carbon Olefins via a Syn-Elimination Approach
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An efficient synthesis of stereodefined tetrasubstituted acyclic all-carbon olefins has been developed via a bis(2,6-xylyl)phosphate formation of stereoenriched tertiary alcohols, followed by in situ syn-elimination of the corresponding phosphates under mild conditions. This chemistry tolerates a wide variety of electronically and sterically diverse substrates and generates the desired tetrasubstituted olefins in high yields and stereoselectivities (>95:5) in most cases. This stereocontrolled olefin synthesis has been applied to the synthesis of anticancer drug tamoxifen in three steps from commercially available 1,2-diphenylbutan-1-one in 97:3 stereoselectivity and 78% overall yield.
- Lim, Ngiap-Kie,Weiss, Patrick,Li, Beryl X.,McCulley, Christina H.,Hare, Stephanie R.,Bensema, Bronwyn L.,Palazzo, Teresa A.,Tantillo, Dean J.,Zhang, Haiming,Gosselin, Francis
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p. 6212 - 6215
(2017/11/24)
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- Highly Stereoselective Synthesis of Tetrasubstituted Acyclic All-Carbon Olefins via Enol Tosylation and Suzuki-Miyaura Coupling
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A highly stereocontrolled synthesis of tetrasubstituted acyclic all-carbon olefins has been developed via a stereoselective enolization and tosylate formation, followed by a palladium-catalyzed Suzuki-Miyaura cross-coupling of the tosylates and pinacol boronic esters in the presence of a Pd(OAc)2/RuPhos catalytic system. Both the enol tosylation and Suzuki-Miyaura coupling reactions tolerate an array of electronically and sterically diverse substituents and generate high yield and stereoselectivity of the olefin products. Judicious choice of substrate and coupling partner provides access to either the E- or Z-olefin with excellent yield and stereochemical fidelity. Olefin isomerization was observed during the Suzuki-Miyaura coupling. However, under the optimized cross-coupling reaction conditions, the isomerization was suppressed to 5% in most cases. Mechanistic probes indicate that the olefin isomerization occurs via an intermediate, possibly a zwitterionic palladium carbenoid species.
- Li, Beryl X.,Le, Diane N.,Mack, Kyle A.,McClory, Andrew,Lim, Ngiap-Kie,Cravillion, Theresa,Savage, Scott,Han, Chong,Collum, David B.,Zhang, Haiming,Gosselin, Francis
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supporting information
p. 10777 - 10783
(2017/08/15)
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- Divergent Synthetic Access to E- and Z-Stereodefined All-Carbon-Substituted Olefin Scaffolds: Application to Parallel Synthesis of (E)- and (Z)-Tamoxifens
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A highly substrate-general synthesis of all-carbon-substituted E- and Z-stereodefined olefins is performed. The method comprises two sets of parallel and stereocomplementary preparations of (E)- and (Z)-α,β-unsaturated esters involving two robust and distinctive reactions: 1) stereocomplementary enol tosylations using readily available TsCl/diamine/(LiCl) base reagents, and 2) stereoretentive Negishi cross-coupling using the catalysts [Pd(dppe)Cl2] (for E) and [Pd(dppb)Cl2] (for Z). The present parallel approach is categorized as both type I (convergent approach: 16 examples, 56–87 % yield) and type II (divergent approach: 18 examples, 70–95 % yield). The obtained (E)- and (Z)-α,β-unsaturated ester scaffolds are successfully transformed into various E- and Z-stereodefined known and novel olefins (8×2 derivatization arrays). As a demonstration, application to the parallel synthesis of both (E)- and (Z)-tamoxifens, a representative motif of all-carbon-substituted olefins, is accomplished in a total of eight steps with an overall yield of 58 % (average 93 %) and 57 % (average 93 %), respectively.
- Ashida, Yuichiro,Honda, Atsushi,Sato, Yuka,Nakatsuji, Hidefumi,Tanabe, Yoo
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- Efficient synthesis of polysubstituted olefins using stable palladium nanocatalyst: Applications in synthesis of tamoxifen and isocombretastatin A4
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A phosphine-free stable palladium nanocatalyst was used for an efficient synthesis of polysubstituted olefins from N-tosylhydrazones and aryl iodides. This methodology was successfully utilized in the synthesis of biologically important tamoxifen and isocombretastatin A4. The nanocatalyst was easily recovered and reused without any apparent loss in size and catalytic activity.
- Ganapathy, Dhandapani,Sekar, Govindasamy
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p. 3856 - 3859
(2014/08/18)
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- Synthesis of cis- and trans-tamoxifen
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The synthesis of cis-tamoxifen, non antiestrogenic tetrasubstituted olefin, was achieved via carboalumination of diphenylacetylene as a key step.Conversion to the antiestrogenic trans-tamoxifen was achieved by facile cis-trans isomerization of the corresponding phenol by acid or catalysts.
- Al-Hassan, Mohammed I.
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p. 1247 - 1252
(2007/10/02)
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- Stereoselective Olefin Formation from the Dehydration of 1-(p-Alkoxyphenyl)-1,2-diphenylbutan-1-ols: Application to the Synthesis of Tamoxifen
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Acid-catalysed dehydration of either diastereoisomer of a 1-(p-alkoxyphenyl)-1,2-diphenylbutan-1-ol gives mainly the Z isomer of the but-1-ene via a common carbenium ion intermediate that can be regenerated by protonation of the (Z)- or (E)-butene with fluorosulphonic acid.Highly stereoselective syn eliminations were achieved by treatment of the butan-1-ols with base and carbon disulphide but dehydrations using N,N,N-triethylammonio-N'-methoxycarbonylsulphamidate proceeded mainly via a carbenium ion.Aspects of the stereoselectivity of the reactions are discussed.The methods can be applied to give simple stereoselective syntheses of the anti-cancer drug tamoxifen.
- McCague, Raymond
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p. 1011 - 1016
(2007/10/02)
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- Palladium-Catalyzed cross-coupling og Vinylalanes with aryl halides
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Synthesis of tri-and tetrasubstituted olefins was achieved via palladium-catalyzed cross-coupling of vinylalanes with arylhalides.
- Al-Hassan, Mohammed I.
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p. 1413 - 1420
(2007/10/02)
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- Stereospecific Synthesis of (Z)-Tamoxifen via Carbometalation of Alkynylsilanes
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A sterospecific synthesis of (Z)-tamoxifen, a tetrasubstituted alkene with antiestrogenic activity, is described.The key reaction that establishes the olefin stereochemistry is a carbometalation of phenyl(trimethylsilyl)acetylene with diethylaluminum chloride-titanocene dichloride.A key intermediate that would lead to (E)-tamoxifen was also prepared in an analogous stereospecific manner.
- Miller, R. Bryan,Al-Hassan, Mohammed I.
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p. 2121 - 2123
(2007/10/02)
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- 1,1,2-Triphenylbut-1-enes: Relationship between Structure, Estradiol Receptor Affinity, and Mammary Tumor Inhibiting Properties
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1,1,2-Triphenylbut-1-enes, which are substituted with acetoxy groups on one, two, or three aromatic rings in the para and/or meta positions, were synthesized.The identity of the occurring E and Z isomers were established by 1H NMR spectroscopy.A study on structure-activity relationships was carried out with regard to estradiol receptor affinity and to inhibiting effects on the growth of a postmenopausal human mammary carcinoma implanted in nude mice.The para-substituted compounds generally exhibited a higher receptor affinity and a better antitumor activity than the corresponding meta-substituted ones.The E isomers were superior to the respective Z isomers in those two properties.The tumor-inhibiting effect of the mono-and disubstituted compounds was better than that of the trisubstituted ones.Except for the trisubstituted compounds, they all showed a good correlation between estradiol receptor affinity and antitumor activity.One of the compounds was also tested on the 9,10-dimethylbenzanthracene-induced, hormone-dependent mammary carcinoma of the Spraque-Dawley rat, and the results corresponded to those obtained in the xenograft tumor.
- Schneider, Martin R.,Angerer, Erwin von,Schoenenberger, Helmut,Michel, Ralf Th.,Fortmeyer, H. P.
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p. 1070 - 1077
(2007/10/02)
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