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Diels-Alder products, chromatographic

Chromatographic purification of the Diels-Alder products lla-d and lla -d furnished a mixture of four bridgehead esters and a mixture of four vinyl esters. Treatment of the bridgehead esters with dimethyl sulfate provided product 12, which consisted of a 1 1 mixture of regioisomer 12a and 12b (each a racemic mixture). These two isomers were separated by HPLC to give the pure racemic forms. [Pg.182]

Careful chromatographic and detailed HNMR spectroscopic analysis of the products from the thermolyses of ethyl azidoformate in o-, m- and p-xylene revealed in all cases a mixture of 1 //-azepines.80 In o-xylene, only two of the four possible isomers were separated and characterized, namely, ethyl 4,5-dimethy 1-1 //-azepine-1 -carboxylate (9 %) and ethyl 3,4-dimethyl-l H-azepine-1-carboxylate (7 %). w-Xylene yielded a 2 3 mixture of ethyl 3,5-dimethyl-l//-azepine-1-carboxylate and ethyl 2,4-dimethyl-l//-azepine-l-carboxylate. The 2,4-dimethyl isomer (20 %) can be isolated from the mixture by removal of the 3,5-dimethyl isomer as its Diels-Alder cycloadduct with ethenetetracarbonitrile. p-Xylene gave a mixture of the two possible isomeric azepines which were partially separated by column chromatography. A pure sample of ethyl 2,5-dimethyl-1//-azepine-1-carboxylate (26%) was obtained from the mixture by selective decomposition of the 3,6-dimethyl isomer with refluxing alcoholic potassium hydroxide. [Pg.139]

Kerth etal. have investigated the reactions of 1,2-thiaphospholes as dienophiles in Diels-Alder reactions (see Sections 12.12.6.1.3 and 12.12.6.2.4). The reaction of compound 281 with cyclopentadiene only proceeded at high temperature (120 °C) and produced two products that could be separated chromatographically. The major product, compound 282, was a crystalline solid, and the minor product, compound 283, was isolated as a viscous oil <2003EJ01894>. [Pg.560]

Recently175 fourteen products were separated chromatographically and identified from the reaction of indole with DMAD in the absence of solvent. All were explained as arising from the fumarate 255, which was isolated, or the maleate 256 which was not. These compounds could undergo Diels-Alder reactions with DMAD to yield 265 and 267, respectively, which were not isolated, but on aromatization both would give the carbazole 266, which was the major product obtained. The main product from the fumarate 255 with DMAD is, in fact, 266,... [Pg.323]

Although obtained only in low yields upon troublesome chromatography of product mixtures that contained much polymeric material, the tricyclic benzofuran and benzothiophene lactones (61) were shown to be isolable products from attempted Diels-Alder reactions on the allene ester precursors shown in Equation (32) <85JCS(Pl)747>. Although it was noted in the case of the two thiophenes that the tricyclics appeared to be forming from a precursor (presumably a dihydro form) on the chromatographic column, it was not possible to convert the crude suspected cycloaddition adducts directly into the aromatics by dehydrogenation with DDQ. Complex mixtures were obtained instead. It is possible that the actual dienophiles in these Diels-Alder reactions are alkynes. In a related study, the bis-lactone (62) was also obtained (Equation (33)) <86H(24)88l>. [Pg.892]

For processes in the gas phase, static systems (constant volume and temperature) have been mostly used, and the manometric method has been widely employed for Diels-Alder reactions and for 1,2-cycloadditions " pressure measurements were associated with gravimetric, infrared or gas-chromatographic analyses whenever required by the presence of more than one product. For Diels-Alder reactions only nonmanometric methods were used, either weighing the producF or chemical analysis of iF, or gas chromatography of reactants and product. 1,2-Cyclo self-addition of gaseous benzyne has been kinetically followed by uv spectroscopy-" -. ... [Pg.89]

Reactions in the pure liquid phase, typically the cyclopentadiene dimerisa-tion, have been sometimes studied by refractometry" " " or dilatometry". In other cases, eithei determination of product and/or reactants has been preferred"" " or the same methods as for reactions in solution were employed. It is worth mentioning that kinetics of a few Diels-Alder reactions were determined by gas-chromatographic analysis of diene, the dienophile being the stationary phase inside the column" . [Pg.89]

A high-performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometric (HPLC/APCI-MS) method has been developed for the determination of the pesticide clofentezine (3,6-bis(2-chlorophenyl)-l,2,4.5-tetrazine) in plum-, strawberry-, and blackcurrant-based fruit drinks <1995RCM1441>. The structural characterization and the mass spectrometric behavior of pyridazinofurocoumarins, prepared by the inverse electron demand Diels-Alder reaction between furocoumarinones and 3,6-bis(methoxycarbonyl)-l,2,4,5-tetrazine, were studied under electron ionization conditions via sequential product ion fragmentation experiments <2004RCM564>. [Pg.647]

Several additional products formed by the Diels-Alder condensations of butadiene and styrene were also characterised by mass spectrometry (MS) and by matching the pyrogram retention times of the samples with retention times obtained for samples spiked with the same dimers. Vapour phase dimerisation of butadiene is known to be a clear-cut bimolecular reaction. Formation of the dimers can take place in the pyrocell as well as in the gas chromatograph (GC) transfer line. Equation 2.4 shows the dimerisation of two molecules of butadiene to form a molecule of 4-vinyl-l-cyclohexene ... [Pg.47]

When conventional Diels-Alder reaction conditions were employed (entries 1 and 2), a chromatographically inseparable mixture of stereoisomers 3.20/3.21 (R = Et) was obtained. Unfortunately, only 3.20 could be used for their proposed synthesis of glaucarubinone. This posed an interesting stereocontrol problem since the formation of both products involved secondary orbital (endo) overlap of the diene with an activating group - the former with the ketone and the latter with the aldehyde. [Pg.18]

As in the previous route (27), the key step in this synthesis was the Diels-Alder reaction between the diene (467), chromatographically separated from the Z-isomer (468), and dimethyl acetylenedicarboxylate. The presence of the 3-methoxy group in (467) allows elimination of methanol from the Diels-Alder adduct (469) to give the aromatized dibenzofuran (465) as the isolated product. This eliminates the bromination/dehydrobromination steps of the original synthesis (27). [Pg.204]


See other pages where Diels-Alder products, chromatographic is mentioned: [Pg.456]    [Pg.236]    [Pg.236]    [Pg.444]    [Pg.85]    [Pg.51]    [Pg.103]    [Pg.53]    [Pg.12]    [Pg.672]    [Pg.131]    [Pg.168]    [Pg.621]    [Pg.131]    [Pg.193]    [Pg.150]    [Pg.35]    [Pg.432]    [Pg.61]    [Pg.254]    [Pg.262]   


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Diels-Alder products

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