Carbon‐13 nuclear magnetic resonance spectra of methyl 2‐pyronecarboxylates

Reaction of pyran-2-thiones 4 with nitroso derivatives led surprisingly to type-8 (19) adducts which proved to be isomeric with the initially expected primary Diels-Alder cycloadducts 5. Methyl 2-thioxo-2H-pyran-5-carboxylate (40, when reacted with nitrosobenzene at -lo", led quantitatively to the thieto-oxazine intermediate 13, which turned out to be the cornerstone of the complex cycloaddition-rearrangement 5 4 reaction pathway (Scheme 3 ) . Differential scanning calorimetry, as performed for the 18a-19a conversion, permitted to demonstrate that this multistep rearrangement is overall a highly exothermal process, the final product 19 representing an energy-sink along this reaction pathway.

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Cycloaddition of 2H‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Defoin

Augelmann

Fritz

et al. 1985

Helvetica Chimica Acta

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Cycloadditionen von 6H‐1,3,4‐Oxadiazin‐6‐onen (4,5‐Diaza‐α‐pyronen), 15.Reaktionen von 6H‐1,3,4‐Oxadiazin‐6‐onen mit Norbornadien. Ein neuer Weg zu 3,6‐disubstituierten α‐Pyronen

Christl¹,

Bodenschatz²,

Feineis³

et al. 1996

Liebigs Ann./Recl.

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Cycloadditionen von 6H-1,3,4-0xadiazin-6-onen (4,5-Diaza-a-pyronen), 1 5L01 Reaktionen von 6H-1,3,4-0xadiazin-6-onen mit Norbornadien. Ein neuer Weg zu 3,6-disubstituierten a-Pyronen* Upon reaction with norbornadiene, ten disubstituted 1,3,4-strates in the absence of boron trifluoride-ether, was aloxadiazin-6-ones l were converted into 3,6-disubstituted a-lowed to react with the Lewis acid. Without use of an acid, pyrones 6. For this purpose, solutions of the substrates were only 6f could be obtained free from further compounds, treated with boron trifluoride-ether or trifluoroacetic acid. whereas in the other cases enol lactones and 1 : 2 products of The smooth formation of 6 was also observed when a y-0x0 the types 8 and 7 were formed additionally. Oxadiazinone ketene, initially generated by heating a solution of the sub-1 j gave enol lactone 10 in the noncatalysed reaction.

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¹³C NMR investigation of some hetero‐ring substituted 2‐ and 4‐quinolone systems

Coppola¹,

Kahle²,

Shapiro³

1981

Org. Magn. Reson.

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A series of 2-and 4-quinolones substituted in the hetero-ring have been evaluated using 13C NMR techniques. Substituent effects are discussed as an aid to evaluation of potential tautonnerimtion in the 2-quinolone systems. The observed substituent shifts for systems having a hydroxy function at the 4-position in the 2-quinolones can be explained without implementing the tautomerism to a 4-quinolone.During the course of some synthetic investigations involving the preparation of substituted 2-and 4-quinolones, it became necessary to use 13C NMR for the analysis of the products. A search of the literature for model systems revealed that very little work has been done in this area, other than for the parent compounds and some ring methylated derivatives.' It seemed of interest to extend these studies to include compounds substituted in the hetero ring, such as 1 and 2 shown below.From the data given in Table 1 it can readily be observed that several of the I3C chemical shifts vary over a large range. The C-2 and C-3 chemical shifts, which range over 18ppm and 32ppm, respectively, can be explained on the basis of substituent shifts inherent to the type of substitution involved. The N-CH, and C-4 chemical shifts also show a large range, and in both cases the shifts are to higher field than the parent system. The upfield substituent shift reflects the steric environment of these carbons. Interestingly, the N-CH, resonance seems sensitive to electronic effects, as seen in a comparison of shifts for l c and Id. The remaining carbon chemical shifts are much less affected by substituents at C-2 and C-3, with C-4a and C-6 showing the largest variations. In all, the substituent chemical shifts for 1 appear to be unexceptional and, therefore, should be useful for the analysis of the tautomerism possibilities in the 2-quinolones discussed below. 4-QuinolonesThe chemical shift data are given in Table 1, and the system numbering is shown above. The assignments are relatively straightforward and were made by comparison with the parent compound and the unmethylated material previously assigned in the literature.' 2-Quinolones

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Carbon‐13 nuclear magnetic resonance spectra of methyl 2‐pyronecarboxylates

Cited by 14 publications

References 17 publications

Cycloaddition of 2H‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Cycloaddition of 2H‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Cycloadditionen von 6H‐1,3,4‐Oxadiazin‐6‐onen (4,5‐Diaza‐α‐pyronen), 15.Reaktionen von 6H‐1,3,4‐Oxadiazin‐6‐onen mit Norbornadien. Ein neuer Weg zu 3,6‐disubstituierten α‐Pyronen

¹³C NMR investigation of some hetero‐ring substituted 2‐ and 4‐quinolone systems

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Carbon‐13 nuclear magnetic resonance spectra of methyl 2‐pyronecarboxylates

Cited by 14 publications

References 17 publications

Cycloaddition of 2H‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Cycloaddition of 2H‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction

Cycloadditionen von 6H‐1,3,4‐Oxadiazin‐6‐onen (4,5‐Diaza‐α‐pyronen), 15.Reaktionen von 6H‐1,3,4‐Oxadiazin‐6‐onen mit Norbornadien. Ein neuer Weg zu 3,6‐disubstituierten α‐Pyronen

13C NMR investigation of some hetero‐ring substituted 2‐ and 4‐quinolone systems

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¹³C NMR investigation of some hetero‐ring substituted 2‐ and 4‐quinolone systems