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Crude Products (crude + products)
Selected AbstractsAcrolein Diethyl Acetal: A Three-Carbon Homologating Reagent for the Synthesis of ,-Arylpropanoates and Cinnamaldehydes by Heck Reaction Catalyzed by a Kaiser Oxime Resin Derived PalladacycleEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2008Emilio Alacid Abstract A polymer palladacycle derived from Kaiser oxime resin was used as a source of palladium(0) in the chemoselective Heck reaction of acrolein diethyl acetal with aryl halides under ligand-free conditions. The use of typical Heck conditions afforded 3-arylpropionic esters, and the process can be directed to the synthesis of cinnamaldehydes under Cacchi conditions. These processes take place with rather low loading of the catalyst, which can be recovered by simple filtration and reused for at least five runs without competitive dehalogenation. This is the first time that a supported palladium complex has been reused under Cacchi conditions. ICP-OES analyses of the Pd content of the crude products in both transformations indicated lower leaching for the esters than for the aldehydes in the range up to 0.08 ppm for the esters and 0.8 ppm for the aldehydes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Regiospecific Synthesis of 4-Deoxy- D - threo -hex-3-enopyranosides by Simultaneous Activation,Elimination of the Talopyranoside Axial 4-OH with the NaH/Im2SO2 System: Manifestation of the Stereoelectronic EffectEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2006Emanuele Attolino Abstract A new and high-yielding method for the regioselective preparation of 4-deoxy- and 2,4-dideoxy-2-acetamido-,- D - threo -hex-3-enopyranosides has been developed. The process involves a simultaneous activation,elimination of the OH-4 group of ,- D -talopyranosides and 2-acetamido-2-deoxy-,- D -talopyranosides, mediated by the NaH/N,N,-sulfuryldiimidazole system at ,30 °C. The same reaction applied on the analogous ,- D -galactopyranosides takes place without any regioselectivity, affording mixtures of hex-3- and hex-4-enopyranosides. In the case of the methyl 2,3,6-tri- O -benzyl-,- D -talo- and ,- D -galactopyranosides, the corresponding 4- O -imidazylates can be isolated by quenching the reactions at ,30 °C. Upon warming these crude products to room temperature, the ,- talo -4- O -imidazylate gives the corresponding hex-3-eno derivative in very high yield, but its ,- galacto analogue gives the hex-4-enopyranoside enol ether in poor yield. The different regiochemical outcome between the talo and the galacto series has been attributed to the stereoelectronic effect exerted, exclusively in talo -configured compounds, by the axially disposed C-2 electronegative substituent, which selectively accelerates the breaking of the antiperiplanar C(3),H bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Preparation of new N6, 9-disubstituted 2-phenyl-adenines and corresponding 8-azaadenines.: A feasibility study for application to solid-phase Synthesis.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2004A suitably substituted pyrimidine 1 was converted to a number of title compounds. Nucleophilic substitu tion involving the chlorine atoms in 1 by treatment with phenylmethanethiol yielded 2 or 3, depending on the reaction temperature. Treatment of 3 with an amine afforded 6-phenylmethanesulfanyl-N4 -substituted-2-phenyl-pyrimidine-4,5-diamines 4,7. These pyrimidines were converted into 2-phenylpurines 8,11 and 2-phenyl-8-azapurines 12,14, by treatment with triethyl orthoformate in the presence of hydrochloric acid (or acetic anhydride), or with potassium nitrite and acetic acid respectively. The thioether function on C(6) was then converted into a sulfonyl group by oxidation with m -chloroperoxybenzoic acid affording purines 15,18 and their 8-azaanalogs 19,21; these compounds, as crude products, were treated with an amine to yield the corresponding adenines 22,25 or 8-azaadenines 26,31. All reactions were performed under conditions com patible with the possible use of a thiomethyl resin in place of phenylmethanethiol to bind the pyrimidine ring of 1 to a solid phase. [source] Synthesis of A,[1-42] and its derivatives with improved efficiencyJOURNAL OF PEPTIDE SCIENCE, Issue 2 2007Márta Zarándi Abstract It has been proved that the principal component of senile plaques is aggregates of ,-amyloid peptide (A,) in cases of one of the most common forms of age-related neurodegenerative disorders, Alzheimer's disease (AD). Although the synthetic methods for the synthesis of A, peptides have been developed since their first syntheses, A,[1-42] is still problematic to prepare. The highly hydrophobic composition of A,[1-42] results in aggregation between resin-bound peptide chains or intrachain aggregation which leads to a decrease in the rates of deprotection and repetitive incomplete coupling reactions during 9-flurenylmethoxycarbonyl (Fmoc) synthesis. In order to avoid aggregation and/or disrupt internal aggregation during stepwise Fmoc solid phase synthesis and to improve the quality of crude products, several attempts have been made. Since highly pure A, peptides in large quantities are used in biological experiments, we wanted to develop a method for a rational synthesis of human A,[1-42] with high purity and adequate yield. This paper reports a convenient methodology with a novel solvent system for the synthesis of A,[1-42], its N -terminally truncated derivatives A,[4-42] and A,[5-42], and A,[1-42] labeled with 7-amino-4-methyl-3-coumarinylacetic acid (AMCA) at the N -terminus using Fmoc strategy. The use of 10% anisole in Dimethylformamide/Dichloromethane (DMF/DCM) can substantially improve the purity and yield of crude A,[1-42] and has been shown to be an optimal coupling condition for the synthesis of A,[1-42]. Anisole is a cheap and simple aid in the synthesis of ,difficult sequences' where other solvents are less successful in the prevention of aggregation during the synthesis. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd. [source] Application of the anionic homologous Fries-rearrangement to the synthesis of 3-alkylbenzofuran-2(3H)-onesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2008Ugo Azzena Abstract We have developed an effective organometallic-based procedure allowing the employment of 2-methylphenols as easily available starting materials in the synthesis of 3-alkylbenzofuran-2(3H)-ones. The first step of this protocol, an anionic homologous Fries-rearrangement, afforded 2-(2- tert -butyldimethylsilyloxyaryl)acetamides, which were selectively metalated and monoalkylated at the benzylic position. Acidic work-up of crude products afforded the desired heterocycles in satisfactory overall yields. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||