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Reactions with Dienophiles

We have also used poly(propynoic acid) in our studies of the photochemical interaction of PCSs with dienophiles, such as maleic anhydride, tetracyanoethylene, and styrene. This photochemical reaction of Diels-Alder type is accompanied by the breakdown of the conjugation system and the formation of slightly colored adducts266. Together with the cycloaddition reaction, photodegradation of PPA and its adducts takes place. A cycloaddition reaction is always preceded by the formation of a donor-acceptor complex of a PCS with a dienophile. [Pg.31]

The comparison of rates of cycloaddition of maleic anhydride, tetracyanoethylene, and styrene to PPA shows that the latter, irrespective of the presence of electronegative groups, behaves in these reactions not as an electron-poor diene system. This fact, together with the composition of side products (giving evidence of PPA decarboxylation), allows the assumption to be made that the cycloaddition of dienophiles involves mainly decarboxylated polyene sections of cis-transoid structure213, 266. This is in agreement with the fact that PPA with predominant trans-transoid configuration interacts with these dienophiles at a substantially lower rate. The ultimate amounts of the dienophile combined with PPA of this structure is also considerably smaller. [Pg.31]


Aminomethylindoles are particularly important synthetic intermediates. 3-Dimethyl-aminomethylindole (gramine) (153) and especially its quaternary salts readily undergo displacement reactions with nucleophiles (Scheme 60). Indole-2,3-quinodimethanes, generated from 2-methylgramine as shown in Scheme 61, undergo intermolecular cycloaddition reactions with dienophiles to yield carbazole derivatives (82T2745). [Pg.71]

The ability of 1,2 (or l,6)-dihydropyridines to undergo a Diels-Alder reaction with dienophiles such as methyl vinyl ketone, methyl acrylate, and acrylonitrile has been utilized in the synthesis of polyfunctional isoquinuclidine as a key intermediate in the synthesis of aspidosperma- and iboga-type alkaloids (66JA3099). [Pg.272]

Dihydropyridines 28 behave as enamines and undergo [2 - - 2] cycloaddition reactions with dienophiles such as acrylonitrile (29) and dimethyl acetylenedicar-boxylate (32). For instance, A -alkyl-l,4-dihydropyridine 28 reacts with 29 to give... [Pg.275]

Furanophane 8 is reactive and undergoes interesting reactions with dienophiles. The reaction of 8 with dimethyl acetylenedi-carboxylic acid gave a polycyclic compound, as shown in the following equation. The compound was derived by intramolecular Diels-Alder reaction of the initially formed 1 1 adducts (38). [Pg.389]

The intramolecular Diels-Alder reaction has become one of the most promising methods for the construction of complex cyclohexene moieties 104). In view of the fact that cyclobutenes rearrange thermally and conrotatary to butadienes (Eq. (9))8l l05) and their willingness to undergo Diels-Alder reactions with dienophiles (Eq. (10))... [Pg.128]

The furo[3,4- ]pyrroles 132, 133 <2002TL6983>, thieno[2,3-f]furan 134, <1996JOC6166>, and furo[2,3-f]pyrrole 135 <1995T193>, which are mostly less stable than the benzo-fused analogues, were trapped by Diels-Alder reactions with dienophiles followed by elimination of water to give the corresponding indoles 136-139, 140, 141, and benzothiephenes 142, 143, and 144 with good to excellent yields (Scheme 13). [Pg.18]

The Diels-Alder reaction with dienophiles such as maleic anhydride metal salts or soaps or esterified to esters with high softening points. [Pg.140]

Indole-2,3-quinodimethanes, generated from 2-methylgramine, undergo intermolecular cycloaddition reactions with dienophiles similar to that of (325) (82T2745). [Pg.350]

A second type of route from pyrroles to indoles involves construction of a vinylpyrrole suitable for [4 + 2] cycloaddition leading to a dihydro- or tetrahydro-indole (Scheme 19) (80JOC4515, 81T1597). The dihydro systems can be easily aromatized. 2-Nitrovinylpyrroles, which are readily available by condensation of pyrrole-2-carbaldehyde with nitromethane, give fully aromatic indoles on reaction with dienophiles (equation 139) (73JCS(P1)2450). The aromatization results from elimination of nitrous acid and a further dehydrogenation. [Pg.349]

In the fused compounds (241) and (242) the furan ring fails to react as a diene and Diels-Alder reaction with dienophiles occurs on the terminal carbocyclic rings. However, (243) and (244) afford monoadducts with dimethyl fumarate by addition to the furan rings (70JA972). The rates of reaction (Table 2) of a number of dehydroannuleno[c]furans with maleic anhydride, which yield fully conjugated dehydroannulenes of the exo type (247), have been correlated with the aromaticity or antiaromaticity of the products (76JA6052). It was assumed that the transition state for the reactions resembled products to some extent, and the relative rates therefore are a measure of the resonance energy of the products. The reaction of the open-chain compound (250), which yields the adduct (251), was taken as a model. Hence the dehydro[4 + 2]annulenes from (246) and (249) are stabilized compared to (251), and the dehydro[4 ]annulenes from (245) and (248) are destabilized (Scheme 84). [Pg.633]

Benzo[c]pyrylium-3-oxides 240 having an orf/io-quinonoid resonance structure act as dienes in reactions with dienophiles (84TL3659). [Pg.225]

There are only a few reported members of this series. The first mentioned is 3,4,5,6-tetrahydro-3-phenyl-2//-l,2,3-thiadiazine 1,1-dioxide, which is prepared in low yield by cyclization of N-3-chloropropylsulfonyl-N -phenylhydrazine with base (62JPR56). The well-known property of azoalkenes to undergo [4 + 2] cycloaddition reactions with dienophiles can be exploited to give 1,2,3-thiadiazines. Thus, N-phenylazostilbene, PhCH=C(Ph)N=NPh, reacts slowly with sulfine 1 at room temperature to yield the trans (44%) and cis (13%) isomers 2 and 3... [Pg.258]

An interesting reactivity comparison was carried out with l-(l-methyl-2-indolyl)-l-(jV-methyl-2 -pyrrolyl)ethene 57 obtained via the corresponding carbinol. An inspection of its structure suggests that the molecule could react in a cycloaddition reaction as a vinylindole or as a 2-vinylpyrrole. In reactions with dienophiles, which include DMAD, it reacted as a 2-vinylindole, affording a carbazole derivative 58 (89JHC1869). [Pg.351]

The reaction with dienophiles of the sulfur-substituted 3-vinylpyrrole, generated in situ by the alkylation of the 3-thioacetylpyrrole, has also been utilized to obtain indoles. Reactions with dimethyl maleate, dimethyl fumarate, methyl acrylate, acrylonitrile, and acrolein gave the corresponding cycloadducts which were directly transformed to the corresponding indoles by treatment with DDQ (91CPB489). [Pg.373]

Diels-Alder reactions with electron-rich alkenes.1 Simple a,(i-unsaturated im-ines (1-aza-1,3-butadienes) do not undergo Diels-Alder reactions with dienophiles. In contrast, the N-phenylsulfonyl imines derived from an aldehyde or ketone undergo Diels-Alder reactions under forcing conditions with electron-rich dienophiles to... [Pg.310]

The reactivity of the benzo analogue of compound 41, that is, 2//-naphtho[l,2-4]thiete 47, has also been studied. Cycloaddition reactions with dienophiles or heterodienophiles performed in boiling toluene yielded naphtho-condensed sulfur heterocycles (Scheme 5) <1998JHC1505>. [Pg.437]

Vinylcyclopropane 514 undergoes a rhodium catalyzed [5+2] cycloadditon reaction with 6-ethynyl-3,4-dihydropyran to furnish intermediate diene 515 that then undergoes an hDA reaction with dienophiles to afford complex pentacyclic chromans 516, 517 (Scheme 113) <2001AGE3895>. [Pg.525]

It had previously been shown that 2,4,6-triphenyl-l,3-azaarsenin 36 could be converted to highly substituted arsenins 38 via a reaction with dienophiles followed by Alder-Rickert cleavage of the intermediate adduct as illustrated in... [Pg.1045]

Aromaticity prevents thiophene taking part in Diels-Alder reactions, but oxidation to the sulfone destroys the aromaticity because both lone pairs become involved in bonds to oxygen. The sulfone is unstable and reacts with itself but will also do Diels-Alder reactions with dienophiles. If the dienophile is an alkyne, loss of SO2 gives a substituted benzene derivative. [Pg.1164]

Dihydropyridines are reactive 1,3-dienes, but their reactions with dienophiles are strongly dependent on the nature of the latter and the reaction conditions. Thus, l-methyl-l,2-dihydropyridine 539 reacts with methyl acrylate at IOC to give a product of overall [2 + 2] cycloaddition 540 by reaction as an enamine. On the other hand, at +80 C compound 539... [Pg.323]


See other pages where Reactions with Dienophiles is mentioned: [Pg.39]    [Pg.64]    [Pg.31]    [Pg.311]    [Pg.955]    [Pg.28]    [Pg.245]    [Pg.546]    [Pg.39]    [Pg.64]    [Pg.725]    [Pg.467]    [Pg.474]    [Pg.708]    [Pg.274]    [Pg.39]    [Pg.64]    [Pg.725]    [Pg.187]    [Pg.37]   


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