- A Mass Spectrometric Study of the Dimethyl Ester Trimethylsilyl Enol Ether Derivatives of Some 3-Oxodicarboxylic Acids
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The fragmentation pathways for the dimethyl ester trimethylsilyl enol ether derivatives of some 3-oxodicarboxylic acids have been found by using B/E and B2/E linked scans, collisional activated decomposition and isotope substitution techniques.The trimethylsilyloxy group strongly directs the decomposition processes, and induces a fragmentation pattern that intimately reflects the structure of the compounds.
- Svendsen, John S.,Whist, Jon E.,Sydnes, Leiv K.
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- Synthesis of (-)-Flavoskyrins by Catalyst-Free Oxidation of (R)-Configured Dihydroanthracenones in Aqueous Media and Its (Bio)synthetic Implications
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A catalyst-free method for the synthesis of dimeric (-)-flavoskyrins has been developed. It involves the autoxidation of chemoenzymatically synthesized (R)-configured dihydroanthracenones in the presence of molecular oxygen in buffer of pH 6.0 followed by spontaneous [4 + 2] cycloaddition in stereocontrolled exo-anti fashion to form (-)-flavoskyrins. The method is applied to obtain several homo- A s well as heterodimerized flavoskyrins (nine examples) in 27-72% yield and implies the involvement of a similar pathway in the (bio)synthesis of modified bisanthraquinones and their analogues.
- Mondal, Amit,De, Arijit,Husain, Syed Masood
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supporting information
p. 8511 - 8515
(2020/11/12)
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- Monomeric Dihydroanthraquinones: A Chemoenzymatic Approach and its (Bio)synthetic Implications for Bisanthraquinones
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Modified bisanthraquinones are complex dimeric natural products containing a cage-like structural motif. For their biosynthesis, monomeric dihydroanthraquinones have been proposed as key intermediates despite not being isolated from natural sources or synthesized as of yet. Here, isolation and characterization of dihydroemodin, as well as dihydrolunatin, synthesized by a biomimetic and chemoenzymatic approach using NADPH-dependent polyhydroxyanthracence reductase (PHAR) from Cochliobolus lunatus followed by Pb(OAc)4 oxidation is reported. Subsequent dimerization through a hetero-Diels–Alder reaction of the dihydroemodin and dihydrolunatin resulted in (?)-flavoskyrin (68 %) and (?)-lunaskyrin (62 %), respectively. Pyridine treatment of (?)-flavoskyrin and (?)-lunaskyrin gave (?)-rugulosin and (?)-2,2′-epi-cytoskyrin A in 64 % and 60 % yield, respectively, through a cascade that involves two dimeric intermediates. Implications of the described synthesis for the biosynthesis of bisanthraquinones by a combination of enzymatic and spontaneous steps are discussed.
- Saha, Nirmal,Mondal, Amit,Witte, Karina,Singh, Shailesh Kumar,Müller, Michael,Husain, Syed Masood
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supporting information
p. 1283 - 1286
(2018/01/27)
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- New method for asymmetrically synthesizing natural product (-)-Euscapholide isomer
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The invention relates to a new method for asymmetrically synthesizing a natural product (-)-Euscapholide isomer. The method comprises the following steps: carrying out methoxybenzyl group protection on (R)-3-hydroxymethyl butyrate used as an initial raw material, reducing by using diisobutylaluminium hydride, carrying out a Mukaiyama aldol reaction, reducing by using sodium borohydride, carrying out ring closure under acidic conditions, eliminating hydroxyl groups, and deprotecting to complete asymmetric total synthesis of the target molecule 1. The method has the advantages of novel and reasonable synthesis route design, cheap and easily available raw material, simple operating process, mild reaction conditions, efficient completion of the asymmetric total synthesis of the Euscapholide isomer with two chiral centers, and single product configuration.
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Paragraph 0042
(2016/10/08)
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- Regio- and stereoselective nickel-catalyzed homoallylation of aldehydes with 1,3-dienes
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Ni(acac)2 catalyzes homoallylation of aldehydes with 1,3-dienes in the presence of triethylborane. Triethylborane serves as a reducing agent delivering a formal hydride to the C2 position of 1,3-dienes, thus generating a formal homoallyl anion species and enabling the novel homoallylation of aldehydes. The reaction proceeds smoothly at room temperature in the absence of any phosphane or nitrogen ligands and is highly regioselective and stereoselective for a wide variety combination of aldehydes and 1,3-dienes: e.g., isoprene and benzaldehyde combine to give a mixture of anti- and syn-1-phenyl-3-methyl-4-penten-1-ol (2.2) in a ratio of 15:1 in 90% yield. Under the conditions, sterically congested aliphatic aldehydes and ketones show low yields. In such cases, diethylzinc serves as a substitute for triethylborane and yields the expected products in good yields with similarly high regio- and stereoselectivity. 1,3-Cyclohexadiene is one exception among 24 kinds of dienes examined and undergoes allylation (not homoallylation) selectively.
- Kimura, Masanari,Ezoe, Akihiro,Mori, Masahiko,Iwata, Keisuke,Tamaru, Yoshinao
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p. 8559 - 8568
(2007/10/03)
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- Neighboring group participation in Lewis acid-promoted [3 + 4] and [3 + 5] annulations. The synthesis of oxabicyclo[3.n.1]alkan-3-ones
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Lewis acids are employed as catalysts in the annulation of 1,4- and 1,5-dicarbonyl dielectrophiles with bis(trimethylsilyl) end ethers of β-diketones and β-keto esters. A variety of 2-(alkoxycarbonyl)-m-oxabicyclo[3.n.1]alkan-3-ones can be constructed by this process in which two new carbon-carbon bonds are generated. Unusually high regiocontrol is observed, and good to excellent stereochemical control can be achieved at virtually every position on the new carbocycles. Intramolecular neighboring group participation is proposed to explain the unusually high selectivities attained in the annulation reaction.
- Molander, Gary A.,Camera, Kimberly O.
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p. 830 - 846
(2007/10/02)
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- Meerwein Saponification of Alkyl 3-Oxoalkanoates in the Gas Chromatograph
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Alkyl 3-oxoalkanoates decompose by unevitable traces of water in the gas chromatograph to yield the corresponding methyl ketones and alcohols (Meerwein saponification).Decomposition occurs in the hot injector (T= 270 deg C) of the gas chromatograph and also on glass capillary columns (T> 160 deg C).Decomposition in routine work can be avoided by preparing the corresponding 3-trimethylsilyl enol ethers.
- Thoma, Heinz,Spiteller, Gerhard
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p. 1237 - 1248
(2007/10/02)
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- A CLASS OF NEW SILYLATING AGENTS. II. A HIGHLY REACTIVE REAGENT FOR INTRODUCTION OF THE TRIMETHYLSILYL GROUP.
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Trimethylsilyl enol ethers of pentane-2,4-dione and methyl acetoacetate react rapidly with alcohols at room temperature without the need catalytic for assistance to give high isolated yields of trimethylsilyl ethers.
- Veysoglu, Tarik,Mitscher, Lester A.
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p. 1303 - 1306
(2007/10/02)
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