- An improved and practical synthesis route to antiproliferative (±)-shikonin and its O-acyl derivatives
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Shikonin and its O-acyl derivatives are attracting increasing levels of attention among medicinal chemists due to their potencies as highly selective cytotoxic agents against cancer cells. However, providing a large number of shikonin-related samples by organic synthesis remains challenging. In the present study, we developed an improved and practical synthesis route to shikonin derivatives by olefin metathesis that has enabled the gram-scale preparation of a prenylated tetramethylnaphthazaline, a key intermediate in the synthesis of shikonin. In addition, a method for the selective cleavage of the acyl protecting groups at the phenolic positions of tri-O-acylated shikonins has been developed that provides concise routes to diverse O-acylshikonin derivatives.
- Ono, Mana,Abe, Shouki,Higai, Koji,Higashi, Shoko,Saito, Setsuo,Saito, Ryota
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p. 738 - 746
(2020/12/09)
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- Catalytic asymmetric aldehyde prenylation and application in the total synthesis of (-)-rosiridol and (-)-bifurcadiol
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Chiral phosphoric acid-catalyzed asymmetric aldehyde prenylation has been established using an α,α-dimethyl allyl boronic ester. The transformation provides expedient access to a wide array of aryl, heteroaryl, aryl-substituted alkenyl and primary and sec
- Huang, Yi-Yong,Kalita, Subarna Jyoti,Li, Jing-Jie,Li, Wang-Lai,Schneider, Uwe,Zhang, Yu-Long,Zhao, Zhen-Ni
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p. 10030 - 10033
(2020/09/15)
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- Hydroxy-directed, fluoride-catalyzed epoxide hydrosilylation for the synthesis of 1,4-diols
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Abstract A novel highly regioselective, fluoride-catalyzed hydrosilylation of β-hydroxy epoxides has been developed. The reaction is modular and applicable to the synthesis of a broad range of 1,4-diols. Fluoride is crucial for two reasons: First, it promotes the formation of a silyl ether (which contains a Si-H bond) and, second, it enables ring opening by an intramolecular SN2 reaction through activation of the silane. The reaction can be performed under air. A modular, convergent, and stereoselective synthesis of 1,4-diols by epoxide hydrosilylation has been developed (see scheme). The reaction occurs under fluoride catalysis, is high yielding, highly regioselective, and can be carried out on a large scale.
- Zhang, Yong-Qiang,Funken, Nico,Winterscheid, Peter,Gans?uer, Andreas
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supporting information
p. 6931 - 6934
(2015/06/08)
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- Highly regioselective and chemoselective titanocene mediated Barbier-type allylation reactions
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Titanocene carboxylate 1 is an excellent chemoselective reagent for unprecedented α-regioselective Barbier-type reactions. It constitutes the first titanocene(iii) able to tolerate epoxides and readily reduced carbonyl compounds, such as aromatic and α,β-unsaturated aldehydes. The Royal Society of Chemistry.
- Morcillo, Sara P.,Martinez-Peragon, Angela,Jakoby, Verena,Mota, Antonio J.,Kube, Christian,Justicia, Jose,Cuerva, Juan M.,Gansaeuer, Andreas
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supporting information
p. 2211 - 2213
(2014/02/14)
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- Prins cyclization of α-bromoethers under basic conditions
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α-Bromoethers have been found to undergo Prins-type cyclization under basic conditions and without the need to add a promoter. The products are those derived from a Markovnikov addition on the pendant alkene. However, the stereochemistry and even the structure of the products sometimes differ from those expected with the classical Lewis-acid-catalyzed Prins reaction of acetals.
- Arpin, Patrice,Hill, Bryan,Larouche-Gauthier, Robin,Spino, Claude
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p. 1193 - 1201
(2014/01/06)
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- Product selectivity control induced by using liquid-liquid parallel laminar flow in a microreactor
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Product selectivity control based on a liquid-liquid parallel laminar flow has been successfully demonstrated by using a microreactor. Our electrochemical microreactor system enables regioselective cross-coupling reaction of aldehyde with allylic chloride via chemoselective cathodic reduction of substrate by the combined use of suitable flow mode and corresponding cathode material. The formation of liquid-liquid parallel laminar flow in the microreactor was supported by the estimation of benzaldehyde diffusion coefficient and computational fluid dynamics simulation. The diffusion coefficient for benzaldehyde in Bu4NClO4-HMPA medium was determined to be 1.32 × 10-7 cm2 s-1 by electrochemical measurements, and the flow simulation using this value revealed the formation of clear concentration gradient of benzaldehyde in the microreactor channel over a specific channel length. In addition, the necessity of the liquid-liquid parallel laminar flow was confirmed by flow mode experiments.
- Amemiya, Fumihiro,Matsumoto, Hideyuki,Fuse, Keishi,Kashiwagi, Tsuneo,Kuroda, Chiaki,Fuchigami, Toshio,Atobe, Mahito
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scheme or table
p. 4256 - 4265
(2011/07/29)
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- Pt-catalyzed tandem 1,2-acyloxy migration/intramolecular [3 + 2] cycloaddition of enynyl esters
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(Formula Presented) A platinum-catalyzed tandem reaction involving enynyl ester isomerization and subsequent intramolecular [3 + 2] cyclization has been developed. This strategy provides an efficient approach to five-, six-, or seven-membered cyclic polyfunctional compounds. Copyright
- Zheng, Huaiji,Zheng, Jiyue,Yu, Binxun,Chen, Qiang,Wang, Xiaolei,He, Yongping,Yang, Zhen,She, Xuegong
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supporting information; experimental part
p. 1788 - 1789
(2010/04/23)
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- Chemoselective reaction system using a two inlet micro-flow reactor: Application to carbonyl allylation
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A new strategy for chemoselective reaction using a two inlet micro-flow reactor is described. In this system, the combined use of suitable flow mode and corresponding cathode material enables chemoselective cathodic reduction to control the product regios
- Amemiya, Fumihiro,Fuse, Keishi,Fuchigami, Toshio,Atobe, Mahito
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supporting information; experimental part
p. 2730 - 2732
(2010/09/04)
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- New and stereoselective synthesis of 1,4-disubstituted buten-4-ols (homoallylic alcohol α-adducts) from the corresponding γ-isomers (3,4-disubstituted buten-4-ols) via an acid-catalyzed allyl-transfer reaction with aldehydes
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The γ-adducts of homoallylic alcohols 3, derived from aldehydes via the usual reaction with common allylic metals 1, were converted to the corresponding α-adducts 6 by an acid-catalyzed allyl-transfer reaction. In the allyl-transfer reaction, anti-and syn
- Sumida, Shin-Ichi,Ohga, Masanori,Mitani, Junji,Nokami, Junzo
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p. 1310 - 1313
(2007/10/03)
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- Solvolysis of 1-[trans-2-(m- Orp-Substituted Phenyl)cyclopropyl]- 1-methylethyl p-Nitrobenzoates
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The solvolyses of 1-[trans-2-(m- or p-substituted phenyl)cyclopropyl]-1-methylethyl p-nitrobenzoates in 80% aqueous acetone have been studied with regard to both reactivity and product composition. For the less reactive substituents such as m-Br, m-Cl, and m-CF3, the solvolysis products were the corresponding 2-(2-arylcyclopropyl)-2-propanol, indicating the cyclopropylmethyl cation intermediate. The ring-opened products increased as the electron-donating ability of the substituents increased. The application of the Yukawa-Tsuno equation to the reactivity afforded a ρ value of -1.43 and r value of 0.59 with a correlation coefficient of 0.997. A large value of r indicates the presence of the allylic cation intermediate where much more charge develops at the benzylic carbon for the derivatives with electron-donating substituents than is the case for the cyclopropylmethyl cation intermediate. Thus the solvolysis reaction proceeds via two independent pathways: one has a cyclopropyl cation intermediate and the other has a homoallylic cation intermediate.
- Kusuyama, Yoshiaki
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p. 685 - 691
(2007/10/03)
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- Effect of Crown Ethers on the Regioselectivity of Allylation of Benzaldehyde with Allylic Barium Reagents
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An increase of α-regioselectivity was observed in the reaction of allylic barium reagents with aldehydes employing crown ether as an additive. For example, an α/γ regioselectivity was improved to 98/2 from 92/8, when an equimolar amount of 18-crown-6 was added to geranylbarium reagent in THF at -78°C prior to the reaction with benzaldehyde.
- Yanagisawa, Akira,Yamada, Yasuhiro,Yamamoto, Hisashi
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p. 1090 - 1092
(2007/10/03)
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- Scope of alkoxymethyl radical cyclizations
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We have explored different aspects of the cyclization capability of alkoxymethyl radicals and report here a full account of our investigations. The required radicals were generated from (phenylseleno)-methyl ethers (e.g., 6), which were prepared from homoallylic or bis-homoallylic alcohols by a two-step process. The alcohols were alkylated with (iodomethyl)tributylstannane. The stannanes were reacted with n-BuLi, and the resulting α-alkoxyanions were trapped with diphenyldiselenide to give the (phenylseleno)methyl ethers, which were stable to chromatography. When treated with tributyltin hydride, in the presence of a radical initiator, these precursors undergo a smooth cyclization to substituted tetrahydrofurans and tetrahydropyrans. Formation of the cyclization product was found to be the primary pathway even at relatively high tin hydride concentration. The diastereoselectivity of this cyclization was comparable to that observed in other radical cyclizations. The cis selectivity in cyclization of 6 increased gradually (up to 11:1) as the reaction temperature was lowered. The cyclization can be used for the synthesis of bicyclic and tricyclic compounds and can be incorporated in systems capable of tandem cyclizations.
- Rawal,Singh,Dufour,Michoud
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p. 7718 - 7727
(2007/10/02)
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- Regioselective allylation and propargylation using acylsilanes: Facile synthesis of PGE3 and F(3α) methyl ester
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Regioselective allylation and propargylation were achieved using acylsilanes as electrophiles and this methodology was applied to the synthesis of PGE3 and F(3α) methyl ester.
- Yanagisawa,Habaue,Yamamoto
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p. 1969 - 1980
(2007/10/02)
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- New Efficient Electrochemical Allylation of Aldehydes and Ketones with a Cadmium-modified Electrode
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Electrochemical allylation of aldehyde or ketone with allylic halides by the use of a cadmium-modified platinum anode and by alternating the cathode and anode at constant intervals gives high yields of the corresponding homoallyl alcohols.
- Tokuda, Masao,Uchida, Mitsuru,Katoh, Yoshitaka,Suginome, Hiroshi
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p. 461 - 462
(2007/10/02)
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- Propargyl and Allyl Grignard and Zinc Reagents. Regioselective Alkylation and Its Application to the Synthesis of PGE3 and F3α Methyl Ester
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Regioselective propargylation and allylation were achieved using acylsilanes as electrophiles, and this methodology was applied to the synthesis of PGE3 and F3α methyl ester.
- Yanagisawa, Akira,Habaue, Shigeki,Yamamoto, Hisashi
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p. 5198 - 5200
(2007/10/02)
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- Allylic Phosphates as Allyl Anion Synthons. Lithium-induced Allylation of Carbonyl Compounds
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Ultrasonication of allylic phosphates and carbonyl compounds with a lithium powder gave high yields of the corresponding homoallylic alcohols.
- Araki, Shuki,Butsugan, Yasuo
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p. 457 - 458
(2007/10/02)
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- REGIOSPECIFIC AND HIGHLY STEREOSELECTIVE ALLYLATION OF ALDEHYDES WITH ALLYLTRIFLUOROSILANE ACTIVATED BY FLUORIDE IONS.
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Allyltrifluorosilane/CsF systems form pentacoordinate allylsiliconates which undergo chemoselective, regiospecific and highly stereoselective allylation of aldehydes, presumably via six-membered cyclic transition states.
- Kira, Mitsuo,Kobayashi, Mineo,Sakurai, Hideki
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p. 4081 - 4084
(2007/10/02)
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- ALLYL METHYL SELENIDES: VALUABLE REAGENTS FOR THE SYNTHESIS OF ALLYLLITHIUMS AND α-METALLO ALLYL SELENIDES
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Allyl selenides are valuable precursors of allyllithiums and of α-metallated allyl selenides.
- Clarembeau, M.,Krief, A.
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p. 3629 - 3632
(2007/10/02)
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- CARBON-CARBON BOND FORMATION WITH METALLIC MANGANESE
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Metallic manganese is found to reduce allylic bromides and achieve the Barbier-type carbonyl addition of allyl unit.
- Hiyama, Tamejiro,Sawahata, Miwa,Obayashi, Michio
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p. 1237 - 1238
(2007/10/02)
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