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showing 10 items of 1967 documents
Cycloaddition reactions. A new type of cycloadduct from a substituted 2-vinylthiophen and dmad
1987
Abstract Cycloaddition reactions between 2-(1-cyanoallyl)thiophen and the dienophiles diethyl azodicarboxylate, N-phenylmaleimide , methyl propiolate, and dimethyl acetylenedicarboxylate are reported. Products include simple benzo[b] thiophen carboxylates (13,19) and reduced derivatives (8,9,10,12,18), as a mixture of diastereoisomers, except in the adduct with diethyl azodicarboxylate. With dimethyl acetylenedicarboxylate a new type of tricyclic compound was also found (20).
Cycloaddition reactions of 1-tert-butyl-4-vinylpyrazole
1989
1-tert-Butyl-4-vinylpyrazole1 a reacts with dimethyl acetylenedicarboxylate (DMAD), methyl propiolate (MP) and N-phenylmaleimide (NPMI) affording the indazole derivatives2,3, and5 as a result of a Diels-Alder ([4 + 2]) cycloaddition. With diethylazodicarboxylate (DEAZD), tetracyanoethylene (TCNE) and 4-phenyl-1,2,4-triazole-3,5-dione (PTAD) the reaction takes place exclusively through the olefinic substituent and the adducts6,7, and9 were isolated. The alkenylpyrazoles1 b–d reacted withDMAD and N-phenylmaleimide to give polymers.
ChemInform Abstract: Cycloaddition Reactions of 1-tert.-Butyl-4-vinylpyrazole.
1990
1-tert-Butyl-4-vinylpyrazole1 a reacts with dimethyl acetylenedicarboxylate (DMAD), methyl propiolate (MP) and N-phenylmaleimide (NPMI) affording the indazole derivatives2,3, and5 as a result of a Diels-Alder ([4 + 2]) cycloaddition. With diethylazodicarboxylate (DEAZD), tetracyanoethylene (TCNE) and 4-phenyl-1,2,4-triazole-3,5-dione (PTAD) the reaction takes place exclusively through the olefinic substituent and the adducts6,7, and9 were isolated. The alkenylpyrazoles1 b–d reacted withDMAD and N-phenylmaleimide to give polymers.
A remarkable rearrangement during reaction between triazolopyridinium ylides and dimethyl acetylenedicarboxylate
1991
Abstract The ylides from 2-acylmethyltriazolopyridinium salts ( 1 ) react with dimethyl acetylenedicarboxylate in toluene solution to give the 7-pyrroleninylpyrazolo[1,5-a]pyridines ( 5 ).
Cycloaddition Reactions with Vinyl Heterocycles
1995
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…
Cycloaddition reactions of 2-vinylthiophen
1985
Abstract Cycloaddition reactions between 2-vinylthiophen and the dienophiles maleic anhydride, dimethyl acetylenedicarboxylate,' methyl propiolate, and methyl acrylate, are reported. Products include simple benzo[b]thiophen carboxylates (6, 13, 17) and reduced derivatives (3, 4, 18). The acetylenic dienophiles also gave a dihydrobenzthienyl-acrylate (16) or -fumarate (11), and the dithienylcyclohexene esters (7) and (14).
Study of Reactivity in the 1,3-Dipolar Cycloaddition Reactions Leading to New Triazolopyrrolopyrazine Ring Systems
2010
The influence of the structural symmetry of the 2-pi double-reactive-sites component in the 1,3-dipolar cycloaddition reactions, involving nitrilimines as dipoles, was investigated. the experimental data showed that the loss of the symmetry leads to the formation of the monocycloadduct in good yields.
A theoretical study on the regioselectivity of 1,3-dipolar cycloadditions using dft-based reactivity indexes
2004
The regioselectivity for a series of four 1,3-dipolar cycloaddition reactions has been studied using global and local reactivity indexes. The results of the theoretical analysis suggest that for asynchronous cycloadditions associated to polar processes, the regioselectivity is consistently explained by the most favorable two-center interactions between the highest nucleophilic and electrophilic sites of the reagents.
Die kinetik der allendimerisation, ein beitrag zum mechanismus
1971
Zusammenfassung The reaction kinetics of the dimerization of some polyhalogenated allenes with the general formula Cl2CCCCIX (X = Cl, Br, C6H5, COOEt) and of tetrabromoallene was studied by an IR spectrophotometric method. The reaction was found to be of strictly second order kinetics. The activation parameters were determined and the experimental data and the influence of the substituents were discussed in terms of the accepted general theory of allene cycloaddition. All data are in agreement with a non-concerted two-step electrocyclic addition mechanism. Within the experimental limits no paramagnetic species like a diradical could be detected by the ESR-method during the dimerization re…
Balls into non-uniform bins
2014
Balls-into-bins games for uniform bins are widely used to model randomized load balancing strategies. Recently, balls-into-bins games have been analysed under the assumption that the selection probabilities for bins are not uniformly distributed. These new models are motivated by properties of many peer-to-peer (P2P) networks, which are not able to perfectly balance the load over the bins. While previous evaluations try to find strategies for uniform bins under non-uniform bin selection probabilities, this paper investigates heterogeneous bins, where the "capacities" of the bins might differ significantly. We show that heterogeneous environments can even help to distribute the load more eve…