Immobilizing bifunctional phosphines with ethoxysilane groups on silica often leads predominantly, and sometimes quantitatively, to P(V) side products that occupy space on the surface but cannot bind metal complexes. Although this side reaction is well-known, and dreaded because it leads to leaching of adsorbed catalysts that are not bound covalently, the exact nature of the surface-bound side product was not yet known. With the help of polycrystalline model compounds of the types [R3PEt]+X- and [R3POEt]+X- (R=alkyl, aryl; X=Cl-, Br-, I-, BF4-) and their solid-state NMR characteristics [delta(31P), CSA], it is demonstrated that the side product is an ethylphosphonium salt bound to the surface by a siloxide anion, [R3PEt]+[Si-O]-.
Die Alkylierung der niedrigkettigen Alkane (III) mit dem aus Ethylen (I)/HF ‐TaF5 intermediär erzeugten Ethylkation (II) zu den Ethylalkanen (IV) wird untersucht.
The 3-phenylazepino[5,4,3-c,d]indole derivatives 5 and 9-11, representing heterocyclic analogs of the selective dopamine D-1 receptor ligands of the 3-phenylbenzazepine class, were synthesized starting from the indole-4-carboxylate 7. Receptor binding studies employing bovine striatal membranes demonstrated that the test compounds 5, 10, and 11 are able to displace the D-1 selective radioligand [3H]-SCH 23390 as well as the D-2 antagonist [3H]-spiperone. Compound 5b turned out to be the most potent and selective ligand (ki = 1.8 microM for D-1 and ki = 8.9 microM for D-2). It is assumed that the moderate selectivity of 5b is due to the conformational inequality of the 7-membered rings when compared to the benzazepines. This results in a spatial arrangement of the phenyl substituent which is not able to interact with a 'subtype selectivity-inducing site'.
Ausgehend vom Alkohol4 werden die Darstellung des 8-Azatryptophans Azaindol-Derivatives I: Asymmetric Synthesis of a New a-Amino Acid 1 alsRacemat sowie eine asymmetrische Synthese der Aminosaureantipoden la und lb beschrieben: la und Ib lassen sich uber die chiralen Dihydropyrazine 1Oa bzw. 10b in hoher Enantiomerenreinheit (ee > 95 %) darstellen.Starting with the alcohol 4,-a synthesis-of racem. 8-azatryptophane and an asymmetric synthesis of its enantiomers la and lb are described: la and Ib, prepared from the dihydropyrazines 10a or are obtained stereoselectively (ee > 95 %).Tryptophan zeigt als ZNS-gangige Serotoninvorstufe hypnotische und antidepressive Wirkungen. Wir haben uns deshalb rnit der Synthese und pharmakologischen Untersuchungen des 8-AzatryptophansDa bei a-Aminosauren die beiden Antipoden haufig unterschiedliche physiologische Aktivitat zeigen, wurde neben einer Synthese des racem. Pyrazolopyridylalanins 1 auch eine gezielte Darstellung der beiden Enantiomere angestrebt.Die Synthese des heterocyclischen Systems erfolgte nach Huisgen uber eine 1,3-dipolare Cycloaddition des NAminopyridiniumiodids2) rnit Propiolsaureethylester, wobei durch Einleiten von Luftsauerstoff die Ausbeuten erheblich gesteigert werden konnten. Gleichzeitig konnte der uberschufi des Dipolarophils auf 10 % reduziert werden. Das Cycloaddukt 3 lie13 sich rnit Lithiumaluminiumhydrid in guter Ausbeute zum Alkohol 4 reduzieren, dessen direkte uberfuhrung in ein Halogenid-bzw. in die Sulfonsaureester 5a oder 5b nicht gelang, da unkontrollierbare Folgereaktionen stattfanden.
The selectivity of the carbonylation of propane (I) in superacid medium is highly enhanced by the addition of catalytic amounts of bromide (NaBr, Me4NBr, Br2).
Starting from the 1,3-dipolar cycloaddition product 6a the peri-fused beta-ketoester 7 is prepared. 7 is employed as a key intermediate for the synthesis of the D-2 autoreceptor agonist 5. Two alternative approaches are used for installing the amino function: electrophilic amination and Curtius rearrangement. The distribution of charge of the aromatic moiety of 5 has been determined by molecular orbital calculations and compared to the respective values of the ergolines. The results of ab-initio calculations and semi-empirical methods have been compared.
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