Search results for " rearrangement"
showing 10 items of 272 documents
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.
Poly(4-vinylbenzoyl azide): A New Isocyanato Group Generating Polymer
2007
4-Vinylbenzoyl azide was synthesized from p-vinylbenzoic acid and polymerized by free radical polymerization. The obtained polymer contained acyl azide groups which were thermally transformed to the corresponding isocyanato groups. Reactions on these polymers with ethanol, hydroxyethyl methacrylate and 1-pyrene-butanol proceeded quantitatively. Time-resolved FT-IR studies of the reactions with ethanol were carried out by varying the concentration and temperature. The effect of the solvent polarity on the Curtius rearrangement was investigated.
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…
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…
Preparation of 4-substituted 1,3-oxathiolan-5-onesviathe sulphenium ion intermediate generated by the pummerer rearrangement
1993
4-Substituted 1,3-oxathiolan-5-ones have been synthesized via the Pummerer rearrangement from the S-oxide of the parent molecule. The 4,5-dione is obtained in the presence of pyridine N-oxide.
Efficient synthesis of novel pyrido[3,2-d]pyrimidine-2,4-diones
2003
Abstract A series of pyrido[3,2- d ]pyrimidine-2,4-diones 5a – g have been synthesized through conversion of 2,3-pyridinedicarboxylic anhydride 1 into half-ester 2 , subsequent Curtius rearrangement and further reaction with amino acids.
Rearrangement of Germacranolides. Synthesis and Absolute Configuration of Elemane and Heliangolane Derivatives from Cnicin
2003
A study of the Cope rearrangement of 15-oxo-germacranolides to 15-oxo-elemanolides has been carried out. The synthesis of two natural elemanolides, isolated from Centaurea paui, and an efficent isomerization of the C-4/C-5 double bond of 15-oxo-germacranolides to form heliangolides are reported. The absolute configuration of all the compounds has been ascertained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)