Search results for "Nucleophile"
showing 10 items of 385 documents
Studies of Nature of Uncommon Bifurcated I–I···(I–M) Metal-Involving Noncovalent Interaction in Palladium(II) and Platinum(II) Isocyanide Cocrystals
2021
Two isostructural trans-[MI2(CNXyl)2]·I2 (M = Pd or Pt; CNXyl = 2,6-dimethylphenyl isocyanide) metallopolymeric cocrystals containing uncommon bifurcated iodine···(metal–iodide) contact were obtained. In addition to classical halogen bonding, single-crystal X-ray diffraction analysis revealed a rare type of metal-involved stabilizing contact in both cocrystals. The nature of the noncovalent contact was studied computationally (via DFT, electrostatic surface potential, electron localization function, quantum theory of atoms in molecules, and noncovalent interactions plot methods). Studies confirmed that the I···I halogen bond is the strongest noncovalent interaction in the systems, followed …
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…
A DFT Characterization of the Mechanism for the Cycloaddition Reaction between 2-Methylfuran and Acetylenedicarboxylic Acid
1999
The molecular mechanism for the cycloaddition reaction between 2-methylfuran and acetylenedicarboxylic acid (ADA) has been characterized using density functional theory methods at the B3LYP/6-31+G* theory level. An analysis of the results on the reaction pathway shows that the reaction takes place along a stepwise mechanism. The initial step corresponds to the nucleophilic attack of the C5 position of the furan ring to one carbon atom of the conjugated acetylenic system of ADA to give a zwitterionic intermediate. Closure of this intermediate along the nucleophilic attack of the other acetylenic carbon to the substituted C2 position of the furan ring affords the Diels−Alder cycloadduct. Alth…
ChemInform Abstract: 1,5,7-Triazabicyclo[4.4.0]dec-1-ene (TBD), 7-Methyl-TBD (MTBD) and the Polymer-Supported TBD (P-TBD): Three Efficient Catalysts …
2010
Abstract The 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and its 7-methyl derivative (MTBD) have been proven to be of great synthetic utility as catalysts in the nitroaldol (Henry) reaction and for the addition of dialkyl phosphites to a variety of carbonyl compounds. The catalysts were in many cases superior to the parent tetramethylguanidine (TMG). In general the reaction proceeds in a few minutes at 0°C. The polymer-supported-TBD (P-TBD) was also proven to be an efficient promoter of the above cited nucleophilic additions.
ChemInform Abstract: The Allyl Ester as Carboxy-Protecting Group in the Stereoselective Construction of Neuraminic Acid Glycosides.
1989
The application of the allyl-ester moiety as protecting principle for the carboxy group of N-acetylneuraminic acid is described. Peracetylated allyl neuraminate 2 is synthesized by reacting the caesium salt of the acid 1 with allyl bromide. Treatment of 2 with HCl in AcCl or with HF/pyridine gives the corresponding 2-chloro or 2-fluoro derivatives 3 and 4, respectively (Scheme 1). In the presence of Ag2CO3, the 2-chloro carbohydrate 3 reacts with di-O-isopropylidene-protected galactose 5 to give the 2–6 linked disaccharide with the α-D-anomer 6a predominating (α-D/β-D = 6:1; Scheme 2). Upon activation of the 2-fluoro derivative 4 with BF3 · Et2O, the β-D-anomer 6b is formed preferentially (…
Diphosphines of dppf-Type Incorporating Electron-Withdrawing Furyl Moieties Substantially Improve the Palladium-Catalysed Amination of Allyl Acetates
2005
Highly active Pd/diphosphine catalytic systems incorporating new, air-stable ferrocenyl-furylphosphines allow nucleophilic allylic amination at room temperature with unprecedented turnover frequencies. For instance, in the presence of 0.01 mol % catalyst the coupling of aniline to allyl acetate occurs at a TOF of more than 10,000 h - 1 ; even the addition of the less nucleophile morpholine to allyl acetate is observed with a TOF of 4250 h - 1 . The amination of the sterically demanding geranyl acetate, a monoterpene derivative of interest in the flavour industry, at low catalyst loadings demonstrates the scope of this methodology, which provides in addition noticeable advantages in terms of…
Der einfluß benachbarter grundbausteine auf die ammonolyse von essigsäureestern phenolischer mehrkernverbindungen
1972
Die Ammonolyse der Essigsaureester verschiedener phenolischer Zwei- und Dreikernverbindungen, die neben Methylphenolbausteinen jeweils einen Nitrophenolbaustein enthalten, wurde untersucht. In allen Fallen wird wie bei einkernigen Nitrophenylestern die Esterbindung im Nitrophenolbaustein ammonolytisch gespalten. Wenn die Bausteine uber Methylenbrucken in ortho-Stellung zu den phenolischen Hydroxylgruppen verknupft sind, werden jedoch auch die Esterbindungen in den Methylphenolbausteinen gespalten, obwohl die Ester von Methylphenolen und Mehrkernverbindungen, die nur Methylgruppen als Substituenten tragen, unter gleichen Bedingungen durch Ammoniak nicht angegriffen werden. In ubereinstimmung…
Photoinduced Molecular Rearrangements. The Photochemistry of Some 1,2,4-Oxadiazoles in the Presence of Nitrogen Nucleophiles. Formation of 1,2,4-Tria…
1996
The photochemistry of some 3,5-disubstituted 1,2,4-oxadiazoles in the presence of nitrogen nucleophiles [external, such as added amines or hydrazines, or internal, such as an o-aminophenyl moiety at C(3) of the oxadiazole ring] has been investigated. In the irradiation of 5-amino-(or 5-N-substituted amino) 3-phenyl-1,2,4-oxadiazoles in the presence of aliphatic primary amines (or ammonia), photolytic species arising from heterolytic cleavage of the ring O−N bond capture the nucleophilic reagent to give open-chain intermediates, which develop into 1,2,4-triazolin-5-ones. Similarly, irradiations of 3,5-diphenyl-, 3-methoxy-5-phenyl-, and 5-methyl-3-phenyl-1,2,4-oxadiazoles gave 1,2,4-triazole…
Pharmakologisch aktive polymere, 5. Modellreaktionen zur umsetzung von pharmaka und enzymen mit monomeren und polymeren reaktiven estern
1973
Die Darstellung reaktiver Ester der Acryl-, Methacryl- und N-Vinylcarbaminsaure wird beschrieben. Die Verbindungen sind im Gegensatz zu anderen reaktiven Saurederivaten wie Saurechloriden, -anhydriden und Isocyanaten kristalline Monomere, die gut zu handhaben sind. Sie lassen sich leicht zu unvernetzten, loslichen Polymeren homo- und copolymerisieren. Die Copolymerisationsparameter wurden bestimmt. Entsprechend wie die aus der Peptidchemie bekannten reaktiven Ester reagieren sie in monomerer wie in polymerer Form bei niedriger Temperatur selektiv und schonend mit Nucleophilen in guten Ausbeuten, z. B. mit Aminen in wasriger Losung. Dies eroffnet die Moglichkeit zur nebenreaktionsfreien Bind…
ChemInform Abstract: Multi-Arm 1,2,3-Thiadiazole Systems.
2010
Benzene derivatives 2a–c with 6, 4, and 3 side chains bearing terminal 1,2,3-thiadiazole rings, respectively, have been prepared. Alkaline cleavage of 2a–c led to the corresponding alkynethiolates 6a–c, which were trapped by electrophiles such as benzyl bromide or iodomethane. The method provides an alternative to the thermal or photochemical cleavage of 1,2,3-thiadiazoles to thioketenes, which react further with nucleophiles.