Search results for "cycloaddition"
showing 10 items of 392 documents
Understanding the participation of 3-nitropyridine in polar Diels–Alder reactions. A DFT study
2015
The reactivity of 3-nitropyridine acting as an electrophilic dienophile in polar Diels-Alder (P-DA) reactions toward three different dienes of increased nucleophilicity has been theoretically studied using DFT methods at the MPWB1K/6-31G(d) level. It has been observed that this aromatic heterocyclic system suffers cycloaddition reactions yielding isoquinoline derivatives. The present DFT study establishes that while the P-DA reactions with isoprene and 1-methoxy-1,3-butadiene take place through a two-stage one-step mechanism, the use of the strong nucleophilic Danishefsky's diene changes the mechanism to a two-step one with formation of a zwitterionic intermediate. These P-DA reactions are …
Polar Diels–Alder reactions using electrophilic nitrobenzothiophenes. A combined experimental and DFT study
2015
Abstract The reactions between 2- and 3-nitrobenzothiophenes with three dienes of different nucleophilicity, 1-methoxy-3-trimethylsilyloxy-1,3-butadiene, 1-trimethylsilyloxy-1,3-butadiene and isoprene developed in anhydrous benzene and alternative under microwave irradiation with molecular solvents or in free solvent conditions, respectively, for produce dibenzothiophenes permit to conclude that both nitroheterocycles act as electrophile with the cited dienes. In the cases of the dienes 1-methoxy-3-trimethylsilyloxy-1,3-butadiene and 1-trimethylsilyloxy-1,3-butadiene which posses major nucleophilicity the observed product is the normal cycloaddition one. However when the diene is isoprene t…
Reactions of Alkenes and Alkynes with an Acyclic Silylene and Heavier Tetrylenes under Ambient Conditions
2014
Cycloaddition reactions of the acyclic silylene Si(SAriPr4)2 (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) with a variety of alkenes and alkynes were investigated. Its reactions with the alkynes phenylacetylene and diphenylacetylene and the diene 2,3-dimethyl-1,3-butadiene yielded silacycles (AriPr4S)2tiebar above startSi(CH═tiebar above endCPh) (1), (AriPr4S)2tiebar above startSi(PhC═tiebar above endCPh) (2), and (AriPr4S)2tiebar above startSiCH2CMeCMetiebar above endCH2 (3) at ambient temperature. The compounds were characterized by X-ray crystallography, 1H, 13C, and 29Si NMR spectroscopy, and IR spectroscopy. No reaction was observed with more substituted alkenes such as propene, (Z)-2-butene, te…
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.