- Total Synthesis of (+)-Arborisidine
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The first total synthesis of arborisidine, a unique Kopsia indole alkaloid possessing a fully substituted cyclohexanone ring system with two quaternary carbons, has been achieved in seven steps in racemic format from tryptamine and in nine steps in asymmetric format from d-tryptophan methyl ester. Key elements of the design include a carefully orchestrated decyanation protocol to finalize the asymmetric formation of an aza-quaternary center that is challenging to access in optically active format via direct Pictet-Spengler cyclizations with tryptamine, a metal-promoted 6-endo-dig cyclization of an enyne to establish the second core quaternary center, and regiospecific functionalizations of the resultant complex diene to finalize the target structure. The distinct and efficient nature of the developed solution is highlighted by several unsuccessful approaches and unexpected rearrangements.
- Zhou, Zhiyao,Gao, Alison X.,Snyder, Scott A.
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- Total Synthesis of (+)-Arborisidine
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The first total synthesis of arborisidine, a unique Kopsia indole alkaloid possessing a fully substituted cyclohexanone ring system with two quaternary carbons, has been achieved in seven steps in racemic format from tryptamine and in nine steps in asymmetric format from d-tryptophan methyl ester. Key elements of the design include a carefully orchestrated decyanation protocol to finalize the asymmetric formation of an aza-quaternary center that is challenging to access in optically active format via direct Pictet-Spengler cyclizations with tryptamine, a metal-promoted 6-endo-dig cyclization of an enyne to establish the second core quaternary center, and regiospecific functionalizations of the resultant complex diene to finalize the target structure. The distinct and efficient nature of the developed solution is highlighted by several unsuccessful approaches and unexpected rearrangements.
- Zhou, Zhiyao,Gao, Alison X.,Snyder, Scott A.
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supporting information
p. 7715 - 7720
(2019/05/22)
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- Sequential Norrish type II photoelimination and intramolecular aldol cyclization of α-diketones: Synthesis of polyhydroxylated cyclopentitols by ring contraction of hexopyranose carbohydrate derivatives
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The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish type II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 °C). Copyright
- Alvarez-Dorta, Dimitri,Leon, Elisa I.,Kennedy, Alan R.,Martin, Angeles,Perez-Martin, Ines,Riesco-Fagundo, Concepcion,Suarez, Ernesto
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supporting information
p. 10312 - 10333
(2013/09/02)
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- Method of preparation of an alkyne with an optically active hydroxyl group in the beta or gamma position of a triple bond and intermediates obtained
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The present invention relates to a method of preparation of an alkyne with an optically active hydroxyl group in the β or γ position of a triple bond and intermediates obtained. The method of the invention for preparation of an alkyne with an optically active hydroxyl group in the β position of a triple bond is characterized in that it comprises the reaction, in the presence of a Lewis acid: of a compound of formula (IV): in which: R is a linear or branched alkyl group having from 1 to 6 carbon atoms. and of a compound of formula (V): [in-line-formulae]R′—C≡C-M ??(V) [/in-line-formulae]in which: R′ represents a hydrogen atom, a linear or branched alkyl group having from 1 to 8 carbon atoms, preferably a methyl group or a trialkylsilyl group. M represents a metal, preferably a metal of group (Ia) of the periodic table, preferably lithium. Another object of the invention comprises the production of an alkyne with an optically active hydroxyl group in the γ position of a triple bond by isomerization of an alkyne with an optically active hydroxyl group in the β position previously obtained.
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Page/Page column 7
(2010/11/25)
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- Novel aliphatic compounds, process for their preparation and their usage
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The present invention provides an aliphatic compound represented by the following formula (I) or pharmacologically acceptable salts thereof: where n denotes an integer of 1 to 11, and 1 denotes an integer of 1 to 16, the aliphatic compound being an optical isomer of the (2R,3S,2′S) configuration when the 8-position thereof is a double bond, or an optical isomer of the (2S,3R,2′RS) configuration when the 8-position is a single bond; methods for producing the compound or pharmacologically acceptable salts thereof; and uses of the compound in the treatment of cardiovascular diseases (e.g. arteriosclerosis, cardiac diseases), cancer, rheumatism, diabetic retinopathy, and respiratory diseases.
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Page/Page column 17-18
(2010/02/05)
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- A Highly Abbreviated Synthesis of Pentalenene by Means of the Squarate Ester Cascade
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(Equation Presented) The sequential addition of 5-methylcyclopentyllithium and propynyllithium to diisopropyl squarate results in the efficient formation of a functionalized angular triquinane having two of its five-membered rings substituted precisely as in the target sesquiterpene. Only seven additional steps are then required to access pentalenene.
- Paquette, Leo A.,Geng, Feng
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p. 4547 - 4549
(2007/10/03)
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- The Synthesis and Molecular Structure of Tetra(isopropyl)silane
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Tetra(isopropyl)silane has been prepared using literature methods, with the individual steps improved by changes in some of the experimental conditions.The key reagent 2-lithiopropene, which can now be obtained in good yields from 1-methacrylic acid via 1,2-dibromo-1-methylpropionic acid and 2-bromopropene by treatment of the latter with ultrasound-activated lithium metal, was shown to contain mono- and dilithiopropyne.The reaction with chlorotrimethylsilane led to the corresponding silylated derivatives, while with silicon tetrachloride tetra(isopropenyl)silane was obtained, which after purification is easily converted into the title compound by catalytic hydrogenation. - The gas phase molecular structure of 4Si has been determined by electron diffraction.The parameters could be successfully refined for a model of S4 symmetry.Bond distances Si-C, C-C, and C-H as well as bond angles Si-C-C and C-C-H show the steric compression of the four isopropyl substituents.Steric strain is minimized by twists of the methyl groups and the isopropyl groups away from the fully staggered conformations, but also by an increase of two of the C-Si-C angles as compared to the remaining four, which are decreased relative to the tetrahedral standard.The structure differs strongly (mainly in the twist angles) from that of the isoelectronic tetra(isopropyl)phosphonium cation in 4P(1+)(1-), but is very similar to those of tetra(cyclohexyl)silane and of tri(isopropyl)phosphonium isopropylide, where the pyramidal configuration of the ylidic carbon atoms leads to a pseudo homoleptic array of the substituents at phosphorus. - Key Words: Conformational analysis / Electron diffraction / Organosilanes / Silane, tetra(isopropyl)-
- Anderson, David G.,Rankin, David W. H.,Robertson, Heather E.,Frazao, Carlos M. F.,Schmidbaur, Hubert
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p. 2211 - 2218
(2007/10/02)
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