Search results for "Isomerization"
showing 10 items of 281 documents
Regio- and stereoselective synthesis of constrained enantiomeric β-amino acid derivatives
2008
Abstract Chlorosulfonyl isocyanate addition to (−)- and (+)-apopinene furnished monoterpene-fused β-lactams in highly regio- and stereospecific reactions. β-Lactams 5 and 13 exhibited reactivities similar to those of the cycloalkane-fused analogs and were easily converted to the β-amino acid and its protected derivatives. The base-catalyzed isomerization of the cis -amino ester afforded the corresponding trans -amino acid enantiomers in excellent yields. The complete isomerization is explained by the stability difference, which was estimated by ab initio calculations between the cis- and trans -diastereomers.
Temperature- and Light-Responsive Polyacrylamides Prepared by a Double Polymer Analogous Reaction of Activated Ester Polymers
2009
Two different series of polyacrylamides containing different amounts of salicylideneaniline moieties have been synthesized via a double polymer analogous reaction of poly(pentafluorophenyl acrylate) (PPFPA). All copolymers were designed to exhibit a lower critical solution temperature (LCST) in aqueous solution, which was dependent on (i) the amount of incorporated chromophoric salicylideneaniline groups and (ii) the isomerization state of the respective salicylideneaniline group. Higher LCST values were measured for UV-irradiated solutions of the copolymers in comparison to the nonirradiated copolymer solutions. A maximum difference in the LCST of up to 13 °C was found for poly(N-cycloprop…
Influence of the process variables on the product distribution and catalyst decay during cracking of paraffins
1986
Abstract The influence of the partial pressure of the hydrocarbon, reaction temperature, time on stream and the presence of olefins on the product distribution and the kinetics and decay during the cracking of n-heptane on an REHY zeolite were studied. It was found that the isomerization to cracking ratio depends on the hydrocarbon partial pressure. The active sites for cracking and isomerization are not the same and those for cracking decay faster, the selectivity changing with the degree of decay of the zeolite. The protolytic to β-cracking ratio, and therefore the paraffin to olefin ratio, are a function of the partial pressure of n-heptane. Both reactants and products have a marked infl…
1-Cycloundecen-3-in
1988
Es wird ein Syntheseweg fur (E)-1-Cycloundecen-3-in (E-5) beschrieben (Schema 2). Die extrem gespannte Verbindung isomerisiert sich bei Raumtemperatur mit einer Halbwertszeit von 2.2 h (ΔG≠ = 76 kJ/mol). Durch Rotation um die CC-Doppelbindung entsteht dabei (Z)-1-Cycloundecen-3-in (Z-5), das keine geometrische Ringspannung Eg mehr besitzt.
On the regioselectivity of the Friedländer reaction leading to huprines: stereospecific acid-promoted isomerization of syn-huprines to their anti-reg…
2001
Abstract Racemic 12-amino-6,7,8,11-tetrahydro-7,11-methanocycloocta[ b ]quinoline derivatives ( syn -huprines) substituted at the 9-position with a methyl or ethyl group, and both enantioenriched forms of the 9-ethyl derivative, obtained by chiral MPLC resolution of the racemic mixture, were readily converted to the corresponding anti -isomers (huprines) by stereospecific acid-promoted (AlCl 3 or triflic acid) isomerization of the endocyclic CC double bond from the 9(10)- to the 8(9)-position. These results support the hypothesis that the hitherto unseen syn -huprines are also formed under the usual acidic Friedlander reaction conditions used to prepare the known huprines, but rearrange in…
The conformation cis of N-acetyl-N-methyl-α,β-dehydroalanine N′-methylamide and saturated analogues
2007
A series of three homologous amino acids derivatives: N-acetyl-N-methyl-α,β–dehydroalanine N′-methylamide (1), N-acetyl-N-methyl-L-alanine N′-methylamide (2), and N-acetyl-N-methyl-DL-alanine N′-methylamide have been synthesised. The racemic species undergoes spontaneous separation into L and D-enantiomers. From these two chiral forms, the structure of L-enantiomer (3) was analysed. The molecules of 1 – 3 adopt the cis arrangement of the N-terminal amide bond. The molecular conformations are similar for 1 (φ, ψ = 94.6(1)°, −1.7(1)°) and 3 (φ, ψ = 111.5(1)°, −23.8(1)°), and also 2 (φ, ψ = −114.8(2)°, 29.5(2)°), if inversion through the chiral C2 carbon is considered. They are stabilised by i…
Die Isomerisierung des Linolsäuremethylesters mit Rhodiumkomplexen
1977
Die isolierten Doppelbindungen des Linolsauremethylesters konnen mit Rhodiumkomplexen und Zinn(II)chlorid-Dihydrat als Katalysatorsystem konjugiert werden. Die Abhangigkeit der Reaktion von verschiedenen Phosphor- und Stickstoffliganden am Rhodium wurde untersucht. Tri-p-tolylphosphin als Ligand ergab den aktivsten Katalysator, der auch noch bei 25°C eine wirkungsvolle Isomerisierung bewirkt. The Isomerisation of Linoleic Acid Methyl Ester with Rhodium Complexes The isolated double bonds of the linoleic acid methyl ester were conjugated with rhodium complexes plus SnCl2 · 2H2O as catalysts. The dependence of the reaction on phosphorous and nitrogen ligands was studied. The most active catal…
Redox-induced coordination isomerization of a phosphoniobenzophospholide.
2003
1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a…
Synthetic Approaches to Anti-Inflammatory Macrolactones of the Oxacyclododecindione Type
2015
Various synthetic approaches to the oxacyclododecindione-type macrolactones, known for their potent anti-inflammatory activity, are presented. These include an attempted carbonylative ring closure, a hydroacylation route, and an approach by ring-closing metathesis and double bond isomerization, as well as a strategy including ring-closing metathesis/unsaturation. The last route allowed the preparation of a bioactive analogue of the recently described 14-deoxyoxacyclododecindione.
ChemInform Abstract: Synthetic Approaches to Antiinflammatory Macrolactones of the Oxacyclododecindione Type.
2015
A variety of attempts to synthesize oxacyclododecindione macrolactones through carbonylative ring-closure, intramolecular alkyne hydroacyalation, and Ru-catalyzed double bond isomerization fails.