- Quassinoid Synthesis. 2. Preparation of a Tetracyclic Intermediate Having the Bruceantin Tetrahydrofuran Ring
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A synthetic approach to the quassinoid compound bruceantin is described.Tricyclic acid 5, prepared from 2-(methoxycarbonyl)cyclohexanone in one step by the method of Fuchs, is converted into ketal lactone 6 and thence into diol 7.The primary hydroxyl may be selectively protected to give any of several derivatives, including the tetrahydropyranyl derivative 10.Allylic oxidation of this substance provides enone 13, which is dehydrated by treatment with 4-(dimethylamino)pyridine in refluxing acetic anhydride to obtain 16.Lithium/ammonia reduction of 16 yields saturated ketone 23, which is carboxylated by the Stiles procedure to obtain the enolic β- keto ester 26.This material is dehydrogenated to 28 by a novel procedure wherein the enol is heated with thionyl chloride and collidine in refluxing carbon tetrachloride.It is proposed that the dehydrogenation occurs by sulfenylation on carbon, followed by pyrolytic elimination of the resulting sulfenyl chloride ( Scheme III ).The elements of the eventual tetrahydropyranone ring are introduced at this stage by reaction of 28 with silyl ketene acetal 29 at high pressure.The product, enol silane 31, is deprotected by treatment with pyridinium p-toluenesulfonate in warm ethanol to obtain 39.Bromocyclization of this material upon treatment with N-bromosuccinimide in tetrahydrofuran affords bromo eter 40, which rearranges to tetrahydrofuran 41 upon being heated at reflux in N,N-dimethylformamide solution.Deprotection of the latter material provides the β-keto ester 42, a viable intermediate for a bruceantin synthesis.
- Kerwin, Sean M.,Paul, Axel G.,Heathcock,Clayton H.
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- Novel imidazobenzazepine derivatives as dual H1/5-HT 2A antagonists for the treatment of sleep disorders
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A novel imidazobenzazepine template (5a) with potent dual H 1/5-HT2A antagonist activity was identified. Application of a zwitterionic approach to this poorly selective and poorly developable starting point successfully delivered a class of high quality leads, 3-[4-(3-R1-2-R-5H-imidazo[1,2-b][2]benzazepin-11-yl)-1-piperazinyl]- 2,2-dimethylpropanoic acids (e.g., 9, 19, 20, and 21), characterized by potent and balanced H1/5-HT2A receptor antagonist activities and good developability profiles.
- Gianotti, Massimo,Corti, Corrado,Fratte, Sonia Delle,Di Fabio, Romano,Leslie, Colin P.,Pavone, Francesca,Piccoli, Laura,Stasi, Luigi,Wigglesworth, Mark J.
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supporting information; experimental part
p. 5069 - 5073
(2010/10/20)
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- Iodine-promoted silylation of alcohols with silyl chlorides. Synthetic and mechanistic studies
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An efficient silylating system for 1°, 2°, and 3° alcohols, consisting of a silyl chloride/N-methylimidazole/iodine, was developed. Synthetic and mechanistic aspects of this new reagent system, and particularly the role of iodine were investigated in detail using 1H NMR spectroscopy.
- Bartoszewicz, Agnieszka,Kalek, Marcin,Stawinski, Jacek
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p. 8843 - 8850
(2008/12/21)
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- Chemistry of N,N-bis(silyloxy)enamines: Part 5 - Interaction with N-trialkylsilylated azoles. Convenient method for the synthesis of α-azolyl-substituted oximes
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Aliphatic nitro compounds can be considered as good precursors of a wide variety of α-azolyl-substituted oximes. The double silylation of convenient aliphatic nitro compounds and the subsequent N,C-coupling of the resulting N,N-bis(silyloxy)enamines 3 with N-silylated azoles 4 lead to the formation of the silylated α-azolylsubstituted oximes 6, which can be smoothly desilylated to give the target α-azolyl-substituted oximes 5. The mechanism of the key step of this process - N,C-coupling - includes the generation of corresponding conjugated nitrosoalkenes 7 (Schemes 4 and 5). The contribution of the chain mechanism in the overall process is considered as well, The studies of the scope and limitations of this reaction, as well as the optimization of its conditions were accomplished. The configuration of the C=N bond in oximes was established by NMR.
- Lesiv, Alexey V.,Ioffe, Sema L.,Strelenko, Yury A.,Tartakovsky, Vladimir A.
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p. 3489 - 3507
(2007/10/03)
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- Effective silylation of carboxylic acids under solvent-free conditions with tert-butyldimethylsilyl chloride (TBDMSCL) and triisopropylsilyl chloride (TIPSCL)
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Varions types of carboxylic acids can be converted effectively to their corresponding TBDMS and TIPS esters using TBDMSCI and TIPSCI in the presence of imidazole under solvent-free conditions. The advantage of this modified method in comparison with that reported by Corey is the elimination of DMF, which eliminates aqueous work-up. The method is not a time-consuming process and the reactions proceed spontaneously. By this method, absolute chemoselectivity for the protection of carboxylic acid functions in the presence of 2°, 3° hydroxyl groups are observed.
- Firouzabadi, Habib,Iranpoor, Naser,Shaterian, Hamid Reza
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- NOVEL TRICHLOROACETYL BASED SILYLATIONS: SIMPLE METHODS FOR t-BUTYLDIMETHYLSILYLATIONS AND FOR THE PROTECTION OF AMINO GROUPS.
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A new reagent for t-butyldimethylsilylation has been developed and the known trimethylsilyl trichloroacetate (1) has been shown to be of use for N-silylating amines.
- Galan, Adam A.,Lee, Thomas V.,Chapleo, Christopher B.
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p. 4995 - 4998
(2007/10/02)
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- Intermolecular Migration of Silyl Groups in (Trimethylsiloxy)enones
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Crossover experiments prove that the silyl groups in quadratic acid bis(trimethylsilyl ester) (1) undergo rapid intermolecular migrations.This causes the two 13C-NMR signals of the fourmembered ring, which appear at 35 deg C as singlets, to coalesce at 83 deg C and to reappear as a single signal above 170 deg C.The activation energy amounts to 16.9 kcal/mol.Other bis(silylated) ketoenols 2,3,4, and 5 show no dynamic effects; nevertheless, they rearrange intermolecularly.
- Reetz, Manfred T.,Neumeier, Guenther
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p. 1234 - 1243
(2007/10/02)
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