Direct Observation of a Carbene−Pyridine Ylide by Matrix IR Spectroscopy. Rearrangements of 2-Pyridylacylcarbenes

Kuhn, Arvid; Plüg, Carsten; Wentrup, Curt

doi:10.1021/ja993859t

Cited by 54 publications

(36 citation statements)

References 14 publications

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“…6b Previously, photolysis of 1 in CH 3 CN solution was found to form both the ketene 2 (eq. 1) and the ylide intermediate 6a, 6c with characteristic long-wavelength UV/Vis absorption, as originally observed by Wentrup et al, upon photolysis of 1 in a matrix at 10 K. 7 The triisopropylsilyl derivative of diazoketone 1 formed the corresponding substituted ylide 6b upon photolysis, and this product was characterized by 1 H and 13 C NMR. 6c On the basis of the observed upfield pyridyl 1 H NMR shifts of 6b together with calculated nucleus independent chemical shifts and calculated bond length alternations, the ylides 6a and 6b and other analogues were proposed to possess significant antiaromatic character.…”

Section: Introductionsupporting

confidence: 57%

Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity

et al. 2014

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Pyrazinylketene (9) and 4-pyrimidinylketene (11), identified by their IR absorption at 2128 and 2130 cm −1 , respectively, are formed in CH 3 CN as transient intermediates by photolysis of the corresponding diazoketones. The corresponding ylides 10 and 12 are formed concurrently as longer-lived intermediates identified by their distinctive IR and UV absorption. Reactions of 2-pyridylketene and of 9 and 11 with diethylamine form initial amide enol intermediates leading to dihydroheteroarene intermediates and then to amides, whereas amide enols are not observed in reactions with n-butylamine. Reactions with water give observable dihydroheteroarenes. 2,5-Bis(ketenyl)pyrazine (33) is formed by photolysis of 2,5-bis(diazoacetyl)pyrazine (32) together with the corresponding bis(ylide) 35. The latter is calculated to have two geometrically isomeric structures (bond-stretch isomers) with similar energies, one with a central six-membered aromatic ring and another with a 10-pi electron aromatic system. Résumé : Le pyrazinylcétène (9) et le 4-pyrimidinylcétène (11), identifiés respectivement par leur pic d'absorption IR à 2 128 et à 2 130 cm −1 , se forment dans l'acétonitrile, comme intermédiaires de transition, par photolyse des diazocétones correspondantes. Les ylures correspondants 10 et 12, qui se forment simultanément comme intermédiaires plus durables, ont été identifiés par leurs pics d'absorption IR et UV distinctifs. Les réactions entre le 2-pyridylcétène, les composés 9 et 11 et la diéthylamine forment initialement des énols d'amides intermédiaires, qui se transforment ensuite en dihydrohétéroarènes intermédiaires, et enfin, en amides, tandis que l'on n'observe pas la formation d'énols d'amides dans les réactions avec la n-butylamine. Dans les réactions avec l'eau, on peut observer la formation de dihydrohétéroarènes. La 2,5-bis(cétényl)pyrazine (33) est formée par photolyse de la 2,5-bis(diazoacétyl)pyrazine (32), en même temps que le bis(ylure) 35 correspondant. On obtient par calcul que ce dernier peut exister sous deux formes isomériques géométriques (isomères d'élongation) d'énergies semblables, l'une étant formée d'un cycle aromatique central à six atomes et l'autre, d'un système aromatique à dix électrons pi. [Traduit par la Rédaction]

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Section: Introductionsupporting

confidence: 57%

Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity

et al. 2014

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“…[154,155] In contrast, matrix photolysis of 2-diazoacetylpyridine (167) yielded ylide 169 in addition to ketene 170. [156] Continued irradiation of 169 led to ring opening with formation of 170. When the carbonyl carbenes 171 were generated in an argon matrix, intramolecular addition to triple bonds (Ǟ 173) was found to compete with Wolff rearrangement (Ǟ 172).…”

Section: Matrix Isolationmentioning

confidence: 99%

100 Years of the Wolff Rearrangement

2002

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The conversion of α‐diazo ketones into ketenes, and products derived therefrom, was discovered by Wolff in 1902. Major applications of the Wolff rearrangement, such as the Arndt−Eistert reaction (homologation of carboxylic acids) and the ring contraction of cyclic ketones, have been with us for some while. Nevertheless, substantial progress has been made recently. The reaction mechanism has been explored by means of matrix isolation, time‐resolved spectroscopy, and computation. Full retention of configuration of the migrating group has been established by using enantioselective chromatography. The Arndt−Eistert reaction has witnessed a renaissance in the field of natural products, in particular β‐amino acids and β‐peptides. Ring‐contracting Wolff rearrangements and ketene cycloadditions have been applied in syntheses of increasingly complex, biologically active target molecules. These accomplishments, as well as unsolved problems, are addressed in the present review. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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“…The dihydropyridine intermediates 2-4 can be assigned as the E-2-4 and Z-2-4 structures, respectively, and their formation in a 28:72 ratio corresponds to the equilibrium ratio of the anti and syn conformations of 2-pyridylketene (2-1) predicted by computations and observed experimentally by trapping in an argon matrix at 10 K (9). However, the conformations of 2-1 may have different reactivities.…”

Section: Discussionmentioning

confidence: 84%

Acid enol and dihydropyridine intermediates in pyridylketene hydration A computational study

Fedorov¹,

Najafian²,

Tidwell³

et al. 2005

Can. J. Chem.

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3-Pyridylketene (3-1) is found experimentally to undergo hydration forming an intermediate acid enol 3-2; whereas 2-and 4-pyridylketenes (2-1 and 4-1), instead, form (carboxymethylene)dihydropyridine intermediates 2-4 and 4-4, which live much longer than 3-2. Density functional calculations have been carried out to elucidate the hydration reactivity of these ketenes, and reveal that the dihydropyridine intermediates 2-4 and 4-4 are more stable than the unobserved acid enols 2-2 and 4-2 by 6.23 and 12.2 kcal/mol, respectively. For 3-1 a pathway was calculated utilizing two H 2 O molecules leading to the acid enol intermediate 3-2, which then forms 3-pyridylacetic acid (3-3). Hydration of 4-pyridylketene involves net 1,6-addition of water, and a pathway involving a bridge of six H 2 O molecules connecting the pyridyl nitrogen and the carbonyl carbon was determined.Résumé : On a démontré expérimentalement que le 3-pyridylcétène (3-1) subit une hydratation qui conduit à la formation d'un intermédiaire acide énolique 3-2 alors que les 2-et 4-pyridylcétènes (2-1 et 4-1) conduisent plutôt à la formation d'intermédiaires (carboxyméthylène)dihydropyridines 2-4 et 4-4 dont les temps de vie sont beaucoup plus longs que celui du composé 3-2. On a effectué des calculs de densité fonctionnelle pour élucider la réactivité de ces cétènes vis-à-vis de l'hydratation et ils ont démontré que les intermédiaires dihydropyridines 2-4 et 4-4 sont beaucoup plus stables que les acides énoliques 2-2 et 4-2 qui n'ont jamais été isolés et que les différences d'énergie sont respectivement de 6,23 et 12,2 kcal/mol. Pour le composé 3-1, on a calculé une voie réactionnelle qui fait appel à deux molécules d'eau et qui conduit à l'intermédiaire acide énolique 3-2 et finalement à l'acide 3-pyridylacétique (3-3). L'hydratation du 4-pyridylcétène implique une addition 1,6 d'eau et on a déterminé une voie réactionnelle impliquant un pont de six molécules d'eau reliant l'azote de la pyridine et le carbone du groupe carbonyle.

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Direct Observation of a Carbene−Pyridine Ylide by Matrix IR Spectroscopy. Rearrangements of 2-Pyridylacylcarbenes

Cited by 54 publications

References 14 publications

Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity

Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity

100 Years of the Wolff Rearrangement

Acid enol and dihydropyridine intermediates in pyridylketene hydration A computational study

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Direct Observation of a Carbene−Pyridine Ylide by Matrix IR Spectroscopy. Rearrangements of 2-Pyridylacylcarbenes

Cited by 54 publications

References 14 publications

Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity

Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity

100 Years of the Wolff Rearrangement

Acid enol and dihydropyridine intermediates in pyridylketene hydration  A computational study

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Acid enol and dihydropyridine intermediates in pyridylketene hydration A computational study