Search results for "arrangement."
showing 10 items of 343 documents
First Electrophilic Substitutions of 3-Substituted Indoles with Diethoxycarbenium Tetrafluoroborate: Functionalized Indole Derivatives
1990
The indoles 2a-2c react with diethoxycarbenium tetrafluoroborate (1) to furnish the indolecarbaldehydes 3a-3d. In the thermodynamically controlled reaction of 3-methylindole (2a) with 1 the tris(indolyl)methane 4 and diskatole (5), are formed in addition. The limitations of these reactions are discussed and evidence is presented for a C-3-ipso-attack and a Wagner-Meerwein rearrangement, respectively, leading to the formation of 3b or 3d. Erste elektrophile Substitution von 3-substituierten Indolen mit Diethoxycarbenium-Tetrafluoroborat: Funktionalisierte Indol-Derivate Die Indole 2a-2c reagieren mit dem per se synthetisierten Diethoxycarbenium-Tetrafluoroborat (1) zu den Indolcarbaldehyden …
Mass spectra of halogenated esters 6—Methyl esters of some trihalogenated propanoic and butanoic acids
1984
The mass spectral fragmentation of trihalogenated methyl esters, formed in the reactions of monochlorinated methyl propenoates and 2-butenoates with Cl2, BrCl and Br2, have been investigated. In most cases α-cleavage gives the base peak, [COOCH3]+, the peaks originating from the subsequent losses of one or two halogen atoms also being abundant. The primary loss of a halogen atom is more prominent in the C4 derivatives, Br˙ and Cl˙ being preferentially lost from the 2- and 3-positions, respectively. The McLafferty rearrangement yields in one case the base peak; the 2-halo compounds could in general be distinguished by that fragmentation. Typical for all 2-bromo-substituted methyl butanoates …
Five-to-Six Membered Ring-rearrangements in the Reaction of 5-Perfluoroalkyl-1,2,4-oxadiazoles with Hydrazine and Methylhydrazine
2006
The hydrazinolysis reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles with hydrazine or methylhydrazine as bidentate nucleophiles has been investigated. The reaction occurred through the addition of the bidentate nucleophile to the C(5)-N(4) double bond of the 1,2,4-oxadiazole followed by ring-opening and ring-closure (ANRORC) involving the second nucleophilic site of the reagent. This ring-closure step could involve either the original C(3) of the 1,2,4-oxadiazole (giving a five-to-five membered ring rearrangement) or an additional electrophilic center linked to it (exploiting a five-to-six membered ring rearrangement). An alternative initial nucleophilic attack may involve the additional elec…
A five-step synthesis of (±)-tylophorine via a nitrile-stabilized ammonium ylide.
2012
The Stevens rearrangement of a nitrile-stabilized ammonium ylide is the key step of a very short and practical synthesis of the phenanthroindolizine alkaloid (±)-tylophorine. The method requires only five linear steps and is devoid of any protecting group manipulations.
On the Dichotomic Behavior of the Z-2,4-Dinitrophenylhydrazone of 5-Amino-3-benzoyl-1,2,4-oxadiazole with Acids in Toluene and in Dioxane/Water: Rea…
2004
The mononuclear rearrangement (MRH) of the Z-2,4-dinitrophenylhydrazone (4a) and of the Z-phenylhydrazone (4b) of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant triazoles 5a and 5b in toluene has been quantitatively investigated in the presence of trichloroacetic acid (TCA) and of piperidine at 313.1 K. While the behavior in the presence of piperidine recalls the one previously evidenced for some Z-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole, the study of the reactivity in the presence of TCA has most interestingly evidenced a general-acid-catalyzed rearrangement for “both” 4a and 4b. Thus, 4a offers the first example of a solvent-dependent dichotomic behavior in MRH processes o…
ChemInform Abstract: Epoxidation of Olefins with a Silica-Supported Peracid.
2012
Anhydrous [2-percarboxyethyl] functionalized silica (2a) is an advantageous oxidant for performing the epoxidation of olefins 1. Epoxides 3 do not undergo the ring-opening reactions catalyzed by the acidic silica surface, except for particularly activated cases such as styrene oxide. The hydrophilic and acidic character of the silica surface does not interfere with the directing effects exerted by allylic H-bond acceptor substituents. The alkenes 1 carrying hydroxyl groups react with silica-supported peracid 2a faster than unsubstituted alkenes, thus reversing the trend known for reactions with soluble peracids. These results are attributed to the H-bond interactions of substrate 1 with the…
Naphthalenophane durch doppelte Photocyclodimerisierung von Distyrylnaphthalinen
1989
Bei der Belichtung von Distyrylnaphthalinen entstehen in regiospezifischen Kopf-Kopf-Cycloadditionen Naphthalenophane. Je nach Stellung der Styryl-Gruppen beobachtet man vollkommen stereospezifische Prozesse (1d 2, 1g 3, 1h 4) und Dimerisierungen mit partiellen Stereoselektivitaten (1b 5–8, 1i 9, 10). Masgeblich sind die Rotamerenpopulation im Ausgangsprodukt 1 und die elektronischen und sterischen Effekte in den Excimeren. Prinzipiell sind Excimere mit paralleler Anordnung moglichst vieler π-Zentren bevorzugt — ein experimenteller Befund, der durch HMO-Rechnungen untermauert wird. Naphthalenophanes by Twofold Photocyclodimerizatio Reactions of Distyrylanaphthalenes Regiospecific head-to-he…
Exploiting the CNC Side Chain in Heterocyclic Rearrangements: Synthesis of 4(5)-Acylamino-imidazoles
2010
A new variation on the Boulton-Katritzky reaction is reported, namely, involving use of a CNC side chain. A novel Montmorillonite-K10 catalyzed nonreductive transamination of a 3-benzoyl-1,2,4-oxadiazole afforded a 3-(alpha-aminobenzyl)-1,2,4-oxadiazole, which was condensed with benzaldehydes to afford the corresponding imines. In the presence of strong base, these imines underwent Boulton-Katritzky-type rearrangement to afford novel 4(5)-acylaminoimidazoles.
ChemInform Abstract: A Stereoselective Synthesis of (+)-Malyngolide via a Ring-Closing Olefin Metathesis.
2000
Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.
Umsetzungen an polyallylalkoholen ein beitrag zur strukturaufklärung der polyacroleine. Polymere acroleine. 23. mitt.
1962
Redoxpolymerisate des Acroleins wurden mit Natriumboranat reduziert und polymere Allylalkohole mit einem Restgehalt von 4 Mol-% Carbonylgruppen erhalten. Sie enthalten auserdem noch etwa 4 Mol-% C—C-Doppelbindungen. Die Polyallylalkohole wurden xanthogeniert und die Zersetzungsgeschwindigkeit im Vergleich zu Propyl- und Polyvinylalkoholxanthogenaten studiert. Neben Aldehydgruppen kommen noch 3–5 Mol-% Ketogruppen in den Redoxpolymerisaten des Acroleins vor. Die Anwesenheit von Doppelbindungen und Ketogruppen in den Polyacroleinen wird durch Nebenreaktionen bei derPolymerisation erklart. Redox-polymers of acrolein were reduced by sodium boranate and polymeric allylic alcohols were obtained w…