Search results for "Diene"
showing 10 items of 623 documents
Vitamin C Loaded Polyethylene: Synthesis and Properties of Precise Polyethylene with Vitamin C Defects via Acyclic Diene Metathesis Polycondensation
2020
A polyethylene-like polymer with an in-chain vitamin C group was synthesized by olefin metathesis polymerization. Here, we describe both the synthesis and a comprehensive physical characterization. Because of the olefin metathesis synthesis, the vitamin C groups are equidistantly arranged in the polyethylene (PE) main chain. Their separation was adjusted to 20 CH2 units. After hydrogenation, a semicrystalline polymer is obtained that is soluble in polar solvents. Because of its size and steric effect, the vitamin C acts as a chain defect, which is expelled from the crystal lattice, yielding a lamellar crystal with a homogeneous thickness corresponding to the interdefect distance. The physic…
An AM1 theoretical study on the effect of Zn2+ Lewis acid catalysis on the mechanism of the cycloaddition between 3-phenyl-1-(2-pyridyl)-2-propen-1-o…
2002
Abstract The mechanism of the Diels–Alder reaction between 3-phenyl-1-(2-pyridyl)-2-propen-1-one and cyclopentadiene has been investigated with the AM1 semiempirical method. Stationary points for two reactive channels, endo - cis and exo - cis , have been characterized. The role of the Lewis acid catalyst has been modeled taking into account the formation of a complex between Zn 2+ and the carbonyl oxygen atom and the pyridyl nitrogen atom of the 3-phenyl-1-(2-pyridyl)-2-propen-1-one system with and without the presence of two molecules of water around the cation. The mechanism of the uncatalyzed reaction corresponds to a concerted process, but in the presence of Lewis acid catalyst the mec…
Theoretical studies on cycloaddition reactions
2014
Cycloaddition reactions represent one of the most powerful processes in organic chemistry. The most common types of cycloaddition reactions are the Diels-Alder (DA) and the 1,3-dipolar cycloaddition reactions (1,3-DCs) which lead to five and six membered rings, respectively. In our ongoing efforts to contribute to the understanding of DA and 1,3-DCs; we studied the following using the B3LYP/6-31G(d) level of theory: 1. The 1,3-DCs of the pyridinium-3-olates and pyrazinium-3-olates with methyl acrylate and methyl methacrylate [1,2]. 2. The competitive hetero-DA and 1,3-DCs of methyl glyoxylate oxime and its tautomeric nitrone with cyclopentadiene in the absence and in the presence of BF3 as …
Understanding the formation of [3+2] and [2+4] cycloadducts in the Lewis acid catalysed reaction between methyl glyoxylate oxime and cyclopentadiene:…
2013
The formation of the formal [3+2] and [2+4] cycloadducts in the Lewis acid (LA) catalysed reaction of cyclopentadiene (Cp, 1) with methyl glyoxylate oxime (MGO, 2a) has been theoretically studied using DFT methods. Coordination of BF3 LA to the oxygen atom of MGO 2a not only increases the electrophilicity of the oxime, but also makes the corresponding tautomeric BF3:nitrone complex 8b the reactive species. The reaction is characterised by the nucleophilic attack of Cp 1 on the carbon atom of the corresponding BF3:nitrone complex 8b. The subsequent ring closure at the end of the reaction allows the formation of the [3+2] or [2+4] cycloadducts. ELF bonding analysis of selected points on the i…
Stable 17-electron Mo(III) complexes containing alkyl ligands
1999
Abstract The alkylation of the half-sandwich complex CpMoCl 2 ( η 4 -diene) (diene=C 4 H 6 , 2,3-Me 2 C 4 H 4 ) affords the first thermally stable 17-electron compounds containing Mo(III)–alkyl bonds.
Synthesis of Trisaccharides by Hetero-Diels–Alder Welding of Two Monosaccharide Units
2012
A new strategy for the synthesis of di- and trisaccharides based on the de novo synthesis of the linking saccharide unit is presented. In this strategy, functionalized monosaccharide building blocks already incorporating the glycosidic linkages are welded together using a metal-catalyzed hetero-Diels–Alder (HDA) reaction to generate a new monosaccharide unit between them. The highest yields and selectivities in the HDA reaction were obtained by using chiral Schiff base chromium complexes. Disaccharide products were accessible by reaction of Danishefsky's diene with acetyl- and benzyl-protected galactoside aldehydes. For the synthesis of trisaccharide products, acetyl-protected glucose or ga…
Application of Furan as a Diene: Preparation of Condensed 1,3-Oxazines by Retro-Diels−Alder Reactions
2004
(Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-en-2-yl)methanol (3) was treated with oxo carboxylic acids [p-toluoylpropionic acid, cis- or trans-(p-toluoyl)cyclohexanecarboxylic acid, -benzoic acid or methanobenzocyclooctenecarboxylic acid] to furnish the oxanorbornene-fused pyrrolo[1,3]oxazine 4, the isoindolo[1,3]oxazines 5 and 6, and the methanobenzocyclooctenepyrrolo[1,3]oxazine 10, together with the retro-Diels−Alder products pyrrolooxazinone 7, oxazinoisoindolones 8 and 9, and oxazinopyrrolobenzocyclooctene 11. On reflux in chlorobenzene, furan was released from the oxanorbornene heterocycles 5 and 10 to give the retro-Diels−Alder products. The structures of the new compounds were establi…
Stereoselective Total Synthesis of the Diastereomeric Tricyclic Alkaloids Tetraponerine-7 and Tetraponerine-8 Using O-Pivaloylated d-Arabinopyranosy…
2015
Based on a diastereoselective domino Mannich–Michael reaction cascade of 2- N -[( S )-3-{(benzyloxycarbonyl)[4-( tert -butyldiphenylsiloxy)butyl]amino}octylidene]-2,3,4-tri- O -pivaloyl-α- d -arabinopyranosylamine with the Danishefsky diene, the major component of the neurotoxic venom of the New Guinean ant Tetraponera punctulata , tetraponerine-8, and its diastereomer tetraponerine-7 were synthesized in pure form. While the Mannich reaction of the arabinosyl imine of the required ( S )-configured β-aminoaldehyde gave the 2-substituted piperidinone precursor of tetraponerine-8 with excellent diastereoselectivity, the analogous Mannich reaction of the ( R )-configured β-aminoaldehyde afforde…
ChemInform Abstract: Cycloaddition Reactions with Vinyl Heterocycles
2010
Publisher Summary The Diels-Alder reaction is one of the most common and elegant methods for the construction of six-membered rings. Although the number of Diels-Alder cycloadditions with open-chain and alicyclic dienes is very large, the number of examples with aromatic heterocyclic compounds is relatively small. The introduction of a vinyl group as a substituent onto a heterocycle increases the number of possible reactions. This new possibility, however attractive for synthetic purposes, is successful only with π-excessive five-membered heterocyclic derivatives with a few exceptions. The chapter discusses the reactions of vinyl heterocycles with carbodienophiles. The endocyclic and exo-en…
Organometallic ABC-triblock copolymers
1998
The interaction of Fe and Pd complexes with double bonds of the polybutadiene (PB) block in polystyrene-polybutadiene-poly(methyl methacrylate) block copolymers has been studied. The incorporation of Fe(CO)3 fragments into the PB bloc was found to result in an increase in its rigidity. The presence of iron or palladium complexes in the PB block affects strongly the morphology of the triblock copolymers.