Search results for "Sigma"
showing 10 items of 346 documents
ChemInform Abstract: Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitr…
2014
When the products of a Strecker reaction of 1,2,3,4-tetrahydroisoquinolines with aromatic aldehydes are quaternized with alkyl triflates and subsequently treated with base, a ring expansion to 6,7,8,13-tetrahydro-5H-dibenzo[c,f]azonine-5-carbonitriles takes place. The nine-membered cyclic products can be obtained in good yields (78–89%) in a process involving the [1,4]-sigmatropic rearrangement of a nitrile-stabilized ammonium ylide. The reaction sequence provides a new, simple, and efficient method for the synthesis of these unusual N-heterocycles.
Flexible Synthesis of Planar Chiral Azoninones and Optically Active Indolizidinones
2014
The flexible synthesis of defined substituted optically active indolizidinones starting from chiral pool (S)-proline and trans 4-hydroxy-(S)-proline is described. Several defined 2-vinylpyrrolidines were generated in short sequences. The aza-Claisen rearrangement using chloro and phenylketene equivalents delivered nine-membered-ring lactams with up to three stereogenic centres and pS-arranged E olefins. Depending on the substitution pattern, certain azoninones had a flexible conformation and showed pS/pR double-bond flipping. Treatment of the unsaturated lactams with the soft electrophile iodine induced diastereoselective transannular ring contractions. Here, the planar chiral arrangement o…
Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitrile-Stabilized Ammoni…
2014
When the products of a Strecker reaction of 1,2,3,4-tetrahydroisoquinolines with aromatic aldehydes are quaternized with alkyl triflates and subsequently treated with base, a ring expansion to 6,7,8,13-tetrahydro-5H-dibenzo[c,f]azonine-5-carbonitriles takes place. The nine-membered cyclic products can be obtained in good yields (78-89%) in a process involving the [1,4]-sigmatropic rearrangement of a nitrile-stabilized ammonium ylide. The reaction sequence provides a new, simple, and efficient method for the synthesis of these unusual N-heterocycles.
A Straightforward Route to Homoallyl-Homocrotylamines Promoted by a Titanium Complex
2012
I�-Allyltitanium complexes, generated in situ from 1,3-dienes and Cp2TiH, react with benzotriazole derivatives to give homoallylic amines in good yields. Under similar conditions, triple cascade reactions (allyltitanation followed by cationic 2-aza-Cope rearrangement followed by a second allyltitanation) occur from bis(benzotriazolyl) compounds affording a straightforward route to homoallyl-(E)-homocrotylamines. A theoretical study provides further insight into the factors that govern the selectivity of this sequence of reactions. The titanium-promoted reductive coupling of 1,3-dienes with bis(benzotriazolyl) compounds as substrates led selectively to homoallyl-homocrotylamines through a tr…
Synthesis of Isoxazoline Derivatives through Boulton-Katritzky Rearrangement of 1,2,4-Oxadiazoles
2013
The base-induced rearrangement of 1,2,4-oxadiazoles into isoxazoline derivatives is reported. This represents the first example of a three-atom side-chain rearrangement that involves a saturated CCO side chain at C-3 of the oxadiazole. Nonaromatic 3-amino-isoxazoline derivatives are obtained in good yields. Interestingly, this reaction occurs through the rearrangement of aromatic oxadiazoles to form less stable bonds than those that are broken.
Zwitterionic Aza-Claisen Rearrangements Controlled by Pyrrolidine Auxiliaries - Useful Key Steps in Convergent Enantioselective Syntheses
2012
Chiral pyrrolidine substituents served as efficient auxiliaries in diastereoselective zwitterionic ketene aza-Claisen rearrangements. Palladium-catalysed N-allylation starting from optically active proline and prolinol derivatives, as well as from (2S,5S)-2,5-dimethoxymethylpyrrolidine, gave various allylamines bearing trisubstituted olefin moieties. Treatment with complex carboxylic acid fluorides in the presence of trimethylaluminium induced activated ketene addition to the nitrogen and subsequent [3,3] sigmatropic rearrangement to give γ,δ-unsaturated amides with excellent simple diastereoselectivities and up to 11:1 auxiliary-induced diastereomeric ratios. Cleavage of the pyrrolidine am…
Mononuclear heterocyclic rearrangement. Part 6 . Studies on base catalysis of the rearrangement of the (Z)-p-nitrophenylhydrazone of 3-benzoyl-5-phen…
1981
Sigma 1 receptora gēna izslēgšanas ietekme uz adipozo audu stromas šūnu diferenciāciju
2020
Cilmes šūnu iegūšanas avoti, diferenciācijas potenciāli un kas to ietekmē, un to izmantošana terapeitiskos nolūkos ir liels diskusiju un izpētes objekts. Viens no variantiem ir no taukaudiem iegūtās stromas šūnas, kuras ir multipotentas cilmes šūnas, kurām ir pierādīta spēja diferencēties pa osteogēno līniju, kā arī adipogēnu, hondrogēnu un miogēnu šūnu tipiem un citiem. Tiek apskatīti faktori, kas var ietekmēt to diferenciāciju. Šī darba mērķis bija gūt labāku ieskatu uz Sigma 1 receptora gēna izslēgšanas jeb inaktivēšanas ietekmi uz adipozo audu stromas šūnu diferenciāciju. Maģistra darba uzdevumi bija papildināt iemaņas darbā šūnu kultūru laboratorijā un apskatīt pieejamo literatūru par …
Study of Σ(1385) and Ξ(1321) hyperon and antihyperon production in deep inelastic muon scattering
2013
Large samples of \Lambda, \Sigma(1385) and \Xi(1321) hyperons produced in deep-inelastic muon scattering off a ^6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of \Sigma(1385)^+, \Sigma(1385)^-, \bar{\Sigma}(1385)^-, \bar{\Sigma}(1385)^+, \Xi(1321)^-, and \bar{\Xi}(1321)^+ hyperons decaying into \Lambda(\bar{\Lambda})\pi were measured. The heavy hyperon to \Lambda and heavy antihyperon to \bar{\Lambda} yield ratios were found to be in the range 3.8% to 5.6% with a relative uncertainty of about 10%. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator.