Search results for "Reaction"
showing 10 items of 6134 documents
Multicomponent Synthesis of Benzothiophen-2-acetic Esters by a Palladium Iodide Catalyzed S-cyclization – Alkoxycarbonylation Sequence
2021
A catalytic carbonylative approach to the multicomponent synthesis of benzothiophene derivatives from simple building blocks [1-(2-(methylthio)phenyl)prop-2-yn-1-ols, carbon monoxide, and an alcohol)] is presented. It is based on an S-cyclization-demethylation-alkoxycarbonylation-reduction sequence promoted by the PdI2/KI catalytic system, occurring under relatively mild conditions (40 atm, 80 °C, 15 h). Benzothiophene-2-acetic esters are obtained in moderate to good yields (35–70%) starting from variously substituted substrates in combination with different alcohols as external nucleophiles (17 examples). (Figure presented.).
Effect of addition of Lewis/Brönsted acids in the asymmetric aldol condensation catalyzed by trifluoroacetate salts of proline-based dipeptides
2012
Abstract Proline-based dipeptides catalyze aldol condensations with good yield and stereoselectivity after addition of zinc or sodium acetate to the trifluoroacetate peptide. The chirality of the N-terminal proline in the catalyst determines the absolute configuration of the aldol product, but stereoselectivity depends on the configuration of both amino acids, and is higher for the enantiomeric pair R–S, S–R. Regarding the nature of the second component, optimal results in both yield and stereoselectivity are obtained when neutral unbranched primary amino acids are used.
Michael additions to double bonds of esters of N-protected (s)-phenylalanyldehydroalanine (X-(s)-Phe-ΔAla-OMe) and its phosphonic acid counterpart (X…
2017
Electrophilic addition of amines, thiols and bromide to the double bonds of model dehydrodipeptides and dehydrophosphonodipeptide was studied. The double bond in these two classes of peptides reacted similarly and gave the same products. These results indicate that dehydropeptides are very good candidates as substrates for modifications of peptide side-chains.
Studies on the Stereoselective Selenolactonization, Hydroxy and Methoxy Selenenylation of α- and β-Hydroxy Acids and Esters. Synthesis of δ- and γ-La…
2003
Abstract The diastereoselective synthesis of hydroxy substituted γ- and δ-lactones was accomplished following two approaches. A 5- or 6-endo cyclization promoted by electrophilic selenium reagents of α- or β-hydroxy acids and a 5- or 6-exo cyclization of hydroxy esters obtained through a diastereoselective hydroxy selenenylation reaction of α- or β-hydroxy esters. Moreover, the diastereoselective methoxy selenenylation of the above compounds was investigated showing a case in which the compound that was unreactive in the hydroxy selenenylation conditions gave, in the methoxy selenenylation conditions, the deprotected diol. The usefulness of the methoxy selenenylation procedure was proven by…
An insight into the synthesis of novel aryl-substituted alicyclic β-amino acid derivatives through substrate-directed palladium-catalysed regio- and …
2015
Novel aryl-substituted alicyclic β-amino acid derivatives were synthesized through substrate-determined palladium-catalysed cross-coupling of aryl iodides with five- or six-membered cycloalkene β-amino esters. The arylations were investigated with different catalysts, solvents, bases and aryl halides, and with some cyclohexene 2-aminocarboxylate isomers. The stereochemistry and the position of the ring olefinic bond of the starting 2-aminocycloalkanecarboxylate influenced the coupling reaction, and predetermined the structure of the arylated product.
Post-synthetic methods for functionalization of imidazole-fused porphyrins
2018
Several methods for the post-synthetic modification of imidazo[4,5-[Formula: see text]]porphyrins are reported. First, a synthetic approach to the isomeric difunctionalized porphyrins, containing two [Formula: see text]-fused 2-aryl-1[Formula: see text]-imidazole cycles at adjacent or opposite pyrrole rings of the macrocycle is developed. The core chemistry of this synthetic route is the transformation of 2-aryl-1[Formula: see text]-imidazo[4,5-[Formula: see text]]porphyrins into corresponding imidazodioxochlorins followed by Debus–Radziszewski condensation with aromatic aldehyde. Next, 2-(4-bromophenyl)-1[Formula: see text]-imidazo[4,5-[Formula: see text]]-5,10,15,20-tetramesitylporphyrin…
Erweiterte Konjugation in unsymmetrischen Stilbenylsquarainen
1998
Extended Conjugation in Stilbenylsquaraines Unsymmetrical 1-aryl-3-stilbenylsquaraines 2a–e and 1,3-bis(stilbenyl)squaraines 3a–c were prepared by CC coupling reactions of the corresponding substituted arenes with derivatives of squaric acid (Schemes 2 and 3). Dialkylamino and alkoxy groups enhance the solubility of these dyes and enlarge the intramolecular charge transfer of these donor–acceptor–donor systems. The extended conjugation of the stilbene units – in comparison with arene building blocks – leads to significant bathochromic shifts in the Vis/NIR absorption spectra.
New syntheses of condensed heterocycles from isoxazole derivatives. V. Pyrrolo[3,4-b]pyridin-4-ones
1977
Hydrogenolysis with Raney-Nickel or iron powder in acetic acid of 2,5-diphenyl-4-nitro-3-(3,5-R,R-4-isoxazolyl)pyrrolyl ketones, prepared by the Grignard reaction of 2,5-diphenylpyrrole and 3,5-R,R-4-isoxazolecarboxilic acid chlorides followed by nitration, afforded directly the desired 6H-pyrrolo[3,4-b ]pyridin-4-ones.
The reaction of 2,4,5,6-tetraaminopyrimidine with chalcones
2000
The reaction of the tetraaminopyrimidine 1 with the chalcones 2a-f yields, in the presence of catalytic amounts of acetic acid, the 1H-pyrimido[4,5-b][1,4]diazepine derivatives 3a-f. The cyclization process consists of a condensation reaction and a Michael type addition.
An Unexpected Three-Component Condensation Leading to Amino- (3-oxo-2,3-dihydro-1H-isoindol-1-ylidene)- acetonitriles
2004
The reaction of 2-carboxybenzaldehyde with primary amines in the presence of cyanide leads to the formation of 2-substituted amino(3-oxo-2,3-dihydro-1H-isoindol-1-ylidene)acetonitriles. These compounds originate from the condensation of 2-carboxybenzaldehyde with the amine and two molecules of hydrogen cyanide and represent a novel class of isoindolinones.