- An efficient, second-generation synthesis of the signature dioxabicyclo[3.2.1]octane core of (+)-sorangicin a and elaboration of the (Z,Z, E)-triene acid system
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An efficient, second-generation synthesis of the signature dioxabicyclo[3.2.1]octane core of (+)-sorangicin A (1), in conjunction with an effective, stereocontrolled protocol to arrive at the requisite (Z,Z,E)-triene acid system has been developed. Highli
- Smith III, Amos B.,Dong, Shuzhi
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supporting information; experimental part
p. 1099 - 1102
(2009/07/25)
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- Solvent-free Mukaiyama aldol reaction of O-silyl dienolates catalyzed by benzoic acid
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The vinylogous aldol reaction of O-silyl dienolates deriving from 2,2-dimethyl-[1,3]-dioxin-4-ones proceeds in moderate to excellent yields in the presence of catalytic amounts of PhCOOH under solvent-free conditions. Modest to good yields can be obtained by using silica gel or 3 ? molecular sieves as heterogeneous catalysts.
- Acocella, Maria Rosaria,Massa, Antonio,Palombi, Laura,Villano, Rosaria,Scettri, Arrigo
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p. 6141 - 6144
(2007/10/03)
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- Phorboxazole B synthetic studies: Construction of C(1-32) and C(33-46) subtargets
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The convergent syntheses of the C(1-32) and C(33-46) domains of phorboxazole B are described. An iterative cyclocondensation strategy exploited the Jacobsen hetero-Diels-Alder (HDA) reaction as a platform for the synthesis of both the C(5-9) and C(11-15) tetrahydropyran rings. The use of 2-silyloxydiene coupling partners bearing an increasing resemblance to the phorboxazole skeleton was found to lead to a reduction in diastereoselectivity, however, in the case of the C(11-15) ring. The coupling of aldehyde 21 and 2-silyloxydiene 20 by this route provided a C(1-32) fragment which was elaborated to the macrolide core of phorboxazole B. The synthesis of the C(33-46) domain involved a Nozaki-Kishi coupling of aldehyde 31 and vinyl iodide 39. The syntheses of 31 and 39 were highly diastereoselective: an Evans [Cu(Ph-pybox)](SbF6)2-catalysed Mukaiyama aldol reaction formed the cornerstone of the synthesis of 31 whilst a Nagao-Fujita acetate aldol reaction provided a convenient means of installing the sole stereogenic centre of 39.
- Paterson, Ian,Steven, Alan,Luckhurst, Chris A.
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p. 3026 - 3038
(2007/10/03)
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- Reference scales for the characterization of cationic electrophiles and neutral nucleophiles
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Twenty-three diarylcarbenium ions and 38 π-systems (arenes, alkenes, allyl silanes and stannanes, silyl enol ethers, silyl ketene acetals, and enamines) have been defined as basis sets for establishing general reactivity scales for electrophiles and nucleophiles. The rate constants of 209 combinations of these benzhydrylium ions and π-nucleophiles, 85 of which are first presented in this article, have been subjected to a correlation analysis to determine the electrophilicity parameters E and the nucleophilicity parameters N and s as defined by the equation log k(20°C)=s(N+E) (Mayr, H.; Patz, M. Angew. Chem., Int. Ed. Engl. 1994, 33, 938-957). Though the reactivity scales thus obtained cover more than 16 orders of magnitude, the individual rate constants are reproduced with a standard deviation of a factor of 1.19 (Table 1). It is shown that the reactivity parameters thus derived from the reactions of diarylcarbenium ions with π-nucleophiles (Figure 3) are also suitable for characterizing the nucleophilic reactivities of alkynes, metal-π-complexes, and hydride donors (Table 2) and for characterizing the electrophilic reactivities of heterosubstituted and metal-coordinated carbenium ions (Table 3). The reactivity parameters in Figure 3 are, therefore, recommended for the characterization of any new electrophiles and nucleophiles in the reactivity range covered. The linear correlation between the electrophilicity parameters E of benzhydryl cations and the corresponding substituent constants σ+ provides Hammett σ+ constants for 10 substituents from -1.19 to -2.11, i.e., in a range with only very few previous entries.
- Mayr,Bug,Gotta,Hering,Irrgang,Janker,Kempf,Loos,Ofial,Remennikov,Schimmel
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p. 9500 - 9512
(2007/10/03)
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- SYNTHESE DE DERIVES DE L'ACIDE PIPECOLIQUE PAR REACTION D'AZA-DIELS-ALDER : CYCLOADDITIONS ACTIVEES PAR L'IODURE DE ZINC ENTRE LA 1-(PHENYL)-ETHYLIMINE DU GLYOXYLATE DE METHYLE ET LES DIENES RICHES EN ELECTRONS
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The methyl N-(1-phenylethyl)-α-iminoacetate undergoes zinc iodide activated aza-Diels-Alder cycloaddition reactions with electron rich conjugated dienes.Cyclic α-amino-acids are formed in good yields, with complete regioselectivity, but the extent of asymmetric induction by the chiral phenethyl group on the nitrogen is low. KEY WORDS: aza-Diels-Alder reactions; heterocyclic α-amino-acids
- Abraham, Herve,Theus, Elisabeth,Stella, Lucien
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p. 361 - 366
(2007/10/02)
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- Aldolisation-type reaction versus Michael-type addition. Hemiacetal vinylogs: Versatile synthons
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Depending on the steric hindrance of the reaction centers, hemiacetal vinylogs 1 in the presence of BF3.OEt2 can, with enol ethers, lead to a Michael-type addition (4) or an aldolisation-type reaction (3). Hemiacetal vinylog 1b always yields the second reaction leading to β-methoxy-γ,δ-ethylenic carbonyl compounds 4 precursors of polyenic carbonyl compounds 5. Crotonaldehyde and methanol can be used instead of compound 1b.
- Duhamel,Guillemont,Poirier,Chabardes
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p. 4197 - 4200
(2007/10/02)
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- SPECIFIC SOLVATION OF β-KETOALDEHYDES. PART II. HYDROXYLIC SOLVENTS
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Solvation of β-ketoaldehydes, RCOCH2CHO (R = Me, Et, i-Pr, t-Bu and Ph) was investigated in water and alcohols (MeOH, EtOH, i-PrOH and t-BuOH).In alcohols influence of R on the degree of solvation (hemiacetal formation) was observed.In t-BuOH solvation does not occur, whereas in water has no influence on this process (gem.-diol formation).In alcohols the degree of solvation decreases when passing from MeOH to i-PrOH.In these solvents, in addition to hemiacetal, formation of β-alkoxyvinyl ketone was observed.In all investigated solvents the presence of E-enol was stated.
- Terpinski, Jacek,Zajaczkowska-Terpinska, Ewa
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