Search results for "Cycloaddition"
showing 10 items of 392 documents
A DFT study of the Huisgen 1,3-dipolar cycloaddition between hindered thiocarbonyl ylides and tetracyanoethylene
2004
Abstract The mechanism for the 1,3-dipolar cycloaddition between the hindered thiocarbonyl ylide 1 and tetracyanoethylene 2 has been studied at the B3LYP/6-31G ∗ level. Formation of the [3+2] cycloadduct 4 takes place through a stepwise mechanism that is initiated by the nucleophilic attack of the thiocarbonyl ylide 1 to the ethylene derivative 2 to give a zwitterionic intermediate IN . The subsequent cyclization of IN yields a seven-membered cyclic ketene imine 6 , which equilibrates with the thermodynamically more stable [3+2] cycloadduct 4 . The computed free energies are in agreement with the experimental outcomes.
Tandem Reactions of 1,2,4-Oxadiazoles with Allylamines
2011
A reaction of 3-chloro-1,2,4-oxadiazoles with allylamine and diallylamine has been investigated. 3,3a,4,5-Tetrahydroisoxazolo[3,4-d]pyrimidines are produced through a tandem ANRORC/[3 + 2]cycloaddition pathway consisting of the addition of allylamine to the 1,2,4-oxadiazole, followed by ring opening, nitrone formation, and finally cycloaddition. 3-N-Allylamino-1,2,4-oxadiazoles were also obtained as minor products through a classical SNAr. Conversely, a reaction with diallylamine produces 3-N,N-diallylamino-1,2,4-oxadiazole and imidazoline through tandem SNAr/aziridination and nucleophilic ring opening.
A bonding evolution theory study of the mechanism of [3+2] cycloaddition reactions of nitrones with electron-deficient ethylenes
2015
The mechanism of zw-type [3+2] cycloaddition (32CA) reactions of nitrones with electron-deficient (ED) ethylenes has been studied using density functional theory (DFT) methods at the MPWB1K/6-31G(d) level of theory. An exploration of the potential energy surfaces associated with the four competitive reactive channels of the 32CA reaction between C-phenyl-N-methyl nitrone and acrolein indicates that the cycloaddition reaction takes place through a one-step mechanism. This cycloaddition reaction presents a moderate meta regioselectivity and a complete endo stereoselectivity, which is diminished in dichloromethane. Analysis of the DFT reactivity indices of the reagents allows an explanation of…
Understanding the Electronic Reorganization along the Nonpolar [3+2] Cycloaddition Reactions of Carbonyl Ylides
2011
[EN] The nonpolar [3+2] cycloaddition (32CA) reaction of the carbonyl ylide (CY) 23 with tetramethylethylene (TME) 24 has been studied with DFT methods at the B3LYP/6-31G* level. This cycloaddition reaction, which has a very low activation energy of 4.7 kcal/mol, takes place through a synchronous transition structure. A topological analysis of the ELF along the 32CA reaction provides a new scope of the electronic structure of CY 23 as a pseudodiradical species offering a sound explanation of the high reactivity of this CY in nonpolar reactions. In addition, this analysis points to the nonparticipation of the oxygen lone pairs in the 32CA reaction. This cycloaddition can be seen as a pseudod…
Hyperbranched polyethylenimine-supported copper(II) ions as a macroliganted homogenous catalyst for strict click reactions of azides and alkynes in w…
2019
Abstract Loading hyperbranched polyethylenimine (PEI) with copper(II) ions leads to the formation of a new water-soluble metallodendritic polymer Cu(II)-PEI that has been found to effectively catalyze the clickable azide-alkyne [3 + 2] cycloaddition reactions in water under ambient conditions, in the lack of any external reducing agent. A positive dendritic effect on the catalyst activity was observed in the click of 1,2,3-triazole by lowering the reduction potential of copper(II) into the in-situ generation of the catalytically active species copper(I). The reaction proceeds straightforwardly to afford the corresponding 1,4-disubstituted-1,2,3-triazole derivatives in a regioselective manne…
Combining Orthogonal Reactive Groups in Block Copolymers for Functional Nanoparticle Synthesis in a Single Step.
2017
We report on the synthesis of polysarcosine-block-poly(S-alkylsulfonyl)-l-cysteine block copolymers, which combine three orthogonal addressable groups enabling site-specific conversion of all reactive entities in a single step. The polymers are readily obtained by ring-opening polymerization (ROP) of corresponding α-amino acid N-carboxyanhydrides (NCAs) combining azide and amine chain ends, with a thiol-reactive S-alkylsulfonyl cysteine. Functional group interconversion of chain ends using strain-promoted azide–alkyne cycloaddition (SPAAC) and activated ester chemistry with NHS- and DBCO-containing fluorescent dyes could be readily performed without affecting the cross-linking reaction betw…
Supramolecular Nanocycles Comprisingβ-Cyclodextrin-click-Ferrocene Units: Rings of Rings of Rings
2010
We applied 1,3-dipolar cycloaddition to bind ethynylferrocene onto 6I-azido-6I-deoxycyclomaltoheptaose under microwave assisted conditions. The process was investigated by (1) H NMR, FT-IR spectroscopy, and MALDI-TOF mass spectrometry. The ability of the synthesized compound to self-organize to cyclic supramolecular structures was investigated by dynamic light scattering measurements and cryo-transmission electron microscopy.
One-step synthesis of multi-alkyne functional hyperbranched polyglycerols by copolymerization of glycidyl propargyl ether and glycidol
2013
By copolymerization of glycidol with the alkyne-containing oxirane monomer glycidyl propargyl ether (GPE), hyperbranched polyglycerol (hbPG) with a defined number of alkyne functionalities (up to 38%) can be obtained in a one-step procedure. The number of alkynes can be adjusted by the glycidol/GPE ratio to provide multi-alkyne functional hbPGs, maintaining the highly branched polyether structure. Interestingly, the acidic proton of the alkyne moiety does not interfere with the proton exchange mechanism during the polymerization of glycidol. By specific modification of the synthesis procedure, crosslinking reactions can be suppressed. The polymers exhibit molecular weights ranging from 1800…
Combining oxyanionic polymerization and click-chemistry: a general strategy for the synthesis of polyether polyol macromonomers
2014
We describe a synthetic pathway to tailor-made amphiphilic macromonomers by a combination of anionic ring-opening polymerization and copper-catalyzed azide–alkyne cycloaddition (CuAAC). Linear polyglycerol and poly(glyceryl glycerol) were synthesized in a controlled manner by anionic ring-opening polymerization of ethoxyethyl glycidyl ether or isopropylidene glyceryl glycidyl ether, respectively, with narrow and monomodal molecular weight distributions (Mw/Mn < 1.20) and molecular weights ranging from 850 g mol−1 to 2500 g mol−1. After end-capping with propargyl bromide and removal of the protecting groups, the hydrophilic precursors were quantitatively clicked to a series of hydrophobic az…
Polymeric nitrones, 1. Synthesis and modification of polymeric nitrones derived from polymerizable aldehydes
1999
The model compound N,C-diphenylnitrone[N-(benzylidene)aniline-N-oxide] (3) was prepared by condensation of benzaldehyde with phenylhydroxylamine to study its thermal stability. X-ray diffraction analysis of a single crystal established the conformation of the nitrone group. A new monomer 4-(methacryloyloxy)benzaldehyde-phenylnitrone (8) was also prepared and could not be polymerized with 2,2′-azobisisobutyronitrile (AIBN) as initiator at 70°C. Under these conditions the nitrone reacted exclusively in an intermolecular 1,3-dipolar cycloaddition to give oligomeric tetrahydro-1,2-oxazoline derivates. The kinetics of the cycloaddition was investigated. Additionally, different (meth)acryl- and s…