Search results for " Rearrangement"
showing 10 items of 272 documents
Titanium complexes for the formation of nitrogen compounds : synthesis of homoallylamines and amidines
2011
Homoallylic amines are key reagents for the formation of a large number of biologically interesting products. Due to the double bond of their allylic moiety, easily functionalisable, they are commonly used in organic synthesis. This research work deals with the synthesis of homoallylic amines thanks to titanium complexes. In fact, the reductive coupling between of imines and dienes promoted by titanium allows the formation of diastereoisomeric homoallylamines syn and anti. The diastereoselectivity of the reaction is directly affected by the nitrogen substituent. Whether it is benzyl or phenyl, the selectivity will be in favour of syn or anti respectively. Moreover, the addition of a the Lew…
Lewis acid-catalyzed Beckmann rearrangement of ketoximes in ionic liquids
2009
Abstract The Beckmann rearrangement of five ketoximes was done in 17 different ionic liquids by using four Lewis acids. The effect of the type of cation and the type of anion in the ionic liquid on the rate of the rearrangement reaction and product composition is compared and discussed. The effects of the hydrophobicity and the hydrogen bonding ability of ionic liquids on the rearrangement of ketoximes were investigated, as well as the catalytical activity of the Lewis acids.
Regio- and stereoselective oxyfunctionalization at C-1 and C-5 in sesquiterpene guaianolides
1998
Abstract The regio- and stereoselective functionalization at C-1 and C-5 positions in a guaiane skeleton by allylic hydroxylation are described. The stereochemistry of the resulting compounds are identical to those of the majority of natural 1- and 5-hydroxy-guaianolides.
Over 30% of patients with splenic marginal zone lymphoma express the same immunoglobulin heavy variable gene: ontogenetic implications.
2012
We performed an immunogenetic analysis of 345 IGHV-IGHD-IGHJ rearrangements from 337 cases with primary splenic small B-cell lymphomas of marginal-zone origin. Three immunoglobulin (IG) heavy variable (IGHV) genes accounted for 45.8% of the cases (IGHV1-2, 24.9%; IGHV4-34, 12.8%; IGHV3-23, 8.1%). Particularly for the IGHV1-2 gene, strong biases were evident regarding utilization of different alleles, with 79/86 rearrangements (92%) using allele *04. Among cases more stringently classified as splenic marginal-zone lymphoma (SMZL) thanks to the availability of splenic histopathological specimens, the frequency of IGHV1-2*04 peaked at 31%. The IGHV1-2*04 rearrangements carried significantly lo…
Synthesis of Fluorinated Indazoles Through ANRORC-Like Rearrangement of 1,2,4-Oxadiazoles with Hydrazine.
2006
A series of 6-substituted fluorinated indazoles has been obtained through an ANRORC-like rearrangement (Addition of Nucleophile, Ring-Opening and Ring-Closure) of 5-tetrafluorophenyl-1,2,4-oxadiazoles with hydrazine. The initial addition of the bidentate nucleophile to the electrophilic C(5) of the 1,2,4-oxadiazole ring, followed by ring opening and ring closure, leads to the formation of fluorinated indazoles in high yield under mild experimental conditions. Functionalization of the C(6) in the final indazole nucleus was preliminarily achieved through a nucleophilic aromatic substitution on the starting 5-pentafluorophenyl-1,2,4-oxadiazole.
The reactivity of 2-vinylindoles with dimethyl acetylenedicarboxylate
1984
Abstract The overall rates of reaction of 1-substltuted-1- (1-methyl-2-indolyl)ethenes with dimethyl acetylenedicarboxylate are considerably lower than those of the corresponding 2-vinyl- pyrroles. Steric interaction between the N-methyl group on the indole ring and the 1-substituent on the ethenyl group prevents the diene system adopting a coplanar cisoid configuration and, thereby, inhibits the π4 + π2 cycloaddition reaction of the system with dimethyl acetylenedicarboxylate. Under such conditions, the indolylethene preferentially undergoes a Michael addition reaction at the 3-position. The π4 + π2 cycloaddition reaction is promoted at elevated temperatures. No evidence was found for a Co…
Regional Susceptibility in VCD Spectra to Dynamic Molecular Motions
2018
Experimental and theoretical studies of the vibrational circular dichroism (VCD) spectrum of 3-methyl-1-(methyldiphenlsilyl)-1-phenylbutan-1-ol, whose absolute configuration is key to elucidating the Brook rearrangement of tertiary benzylic α-hydroxylsilanes, are presented. It is found that the entire OH-bending region in this spectrum—a region that provides important marker bands—cannot be reproduced at all by standard theoretical approaches even though other regions are well described. Using a novel approach to disentangle contributions to the rotational strength of these bands, internal coordinates are identified that critically influence the appearance of this part of the spectrum. We s…
Experimental and DFT Studies on Competitive Heterocyclic Rearrangements. A Cascade Isoxazole-1,2,4-Oxadiazole-Oxazole Rearrangement
2009
The thermal rearrangements of 3-acylamino-5-methylisoxazoles 1 have been investigated under basic and neutral conditions and interpreted with the support of computational data. The density functional theory (DFT) study on the competitive routes available for the base-catalyzed thermal rearrangement of isoxazoles 1 showed that the Boulton-Katritzky (BK) rearrangement, producing the less stable 3-acetonyl- 1,2,4-oxadiazoles 5, is a much more favored process than either the migration-nucleophilic attack-cyclization (MNAC) or the ring contraction-ring expansion (RCRE). In turn, an increase in reaction temperature will promote the MNAC of oxadiazoles 5, producing the more stable 2-acylaminooxazo…
Meinvalda pārgrupēšanās jonu šķidrumu vidē
2016
Meinvalda pārgrupēšanās jonu šķidrumu vidē. Ikkere L.E., darba vadītājs Dr.h.ķīm., prof. Zicmanis A. Bakalaura darbs, 54 lappuses, 24 attēli, 12 tabulas, 42 literatūras avoti, 5 pielikumi. Latviešu valodā. Bakalaura darba literatūras apskatā ir apkopota galvenā informācija par Meinvalda pārgrupēšanās reakcijām, to katalizatoriem, kā arī par jonu šķidrumiem. Laboratorijā tika veikta trīs jonu šķidrumu sintēze. To struktūras tika pierādītas, izmantojot 1H KMR un IS spektroskopijas metodes. Tika piemeklēti piemērotākie gāzu hromatogrāfijas apstākļi, lai noteiktu pārgrupēšanās reakciju izejvielas un produktus. Tika pārbaudīti dažādu anjonu un slāpekli saturošu katjonu jonu šķidrumu izmantošana …
Human papillomavirus:Its identikit and controversial role in oral oncogenesis,premalignant an malignant lesions(Review)
2007
Human papillomaviruses (HPVs) are a group of host-specific DNA viruses, with a remarkable epithelial cell specificity: they have been reported principally in the ano-genital tract, urethra, skin, larynx, tracheo-bronchial and oral mucosa. More than 100 different HPV types have been identified and classified as high (e.g. 16, 18, 31) or low (e.g. 11, 42, 36) -risk (HR and LR), based on their association with cervical carcinoma. The carcinogenic role of HR-HPV revolves mainly around two of its oncoproteins: HPV-E6 which promotes degradation of the p53 tumour suppressor gene product and HPV-E7 which modifies the pRb tumour suppressor gene product, inhibiting the activity of TGF-beta2. Since th…