Gert Kollenz

α-Oxoketenes - Preparation and Chemistry

This review describes the methods of generation of alpha-oxoketenes and their use in synthesis. While the ketenes are often generated in situ without direct proof for their existence, methods used for their direct observation are also emphasized. The most important classes of precursor molecules are 2-diazo-1,3-diketones, 1,3-dioxin-4-ones, 2,3-dihydrofuran-2,3-diones, and beta-ketoacid derivatives. Synthetically useful reactions are nucleophilic additions to give carboxylic acid derivatives which can be subjected to further functional group manipulation, [2 + 2] cycloadditions to give four-membered rings, and [2 + 4] cycloaddition chemistry with a wide variety of double-and triple-bonded dienophiles, resulting in numerous six-membered heterocyclic ring systems.

Reaktionen mit cyclischen Oxalylverbindungen, XXIV. Zur Reaktion von 4-Benzoyl-5-phenyl-furan-2,3-dion mit Phenylhydrazonen bzw. Phenylhydrazin

Abstract4-Benzoyl-5-phenyl-furan-2,3-dione (1) reacts with various phenylhydrazones2 at 60–80°C to the pyrazole carboxylic acid3 a, which then can be decarboxylated to 4-benzoyl-1,5-diphenyl-pyrazole (5).1 and phenylhydrazine combine again yielding3 a as the main product and the isomeric pyridazinone6 as by-product. At higher temperatures (120–140°C) the reaction of1 with2 a leads to the formation of dibenzoyl acetic acid hydrazide derivatives8.The structures of all products were confirmed by IR, MS,15N- and13C-NMR spectroscopic measurements, in the case of the pyridazinone6 also by an X-ray study.6 crystallizes with one moleDMSO monoclinically in space group P 21/n (Nr. 14) with 4 molecules6 andDMSO per cell.The reaction pathways leading to the compounds3, 6 and8 are discussed.

Reactions of cyclic oxalyl compounds, part 29: A simple synthesis of functionalized 1H-pyrimidines

Summary4-Benzoyl-5-phenylfuran-2,3-dione (1) and the semicarbazones2, ureas and thioureas6, respectively, combine with loss of water and carbondioxide yielding the 1H-pyrimidine derivatives3 and7, respectively, in moderate yields (30–75%). Hydrolysis of3 b leads to the 1-amino-pyrimidine-2-one4.Zusammenfassung4-Benzoyl-5-phenylfuran-2,3-dion (1) cyclisiert mit den Semicarbazonen2 sowie den Harnstoffen bzw. Thioharnstoffen6 unter Verlust von H2O und CO2 zu einer Reihe von 1,4,5-substituierten 1H-Pyrimidinen in Ausbeuten von 30–75%. Die an3 b exemplarisch durchgeführte Hydrolyse liefert die 1-Amino-Verbindung4.

Reactions of cyclic oxalyl compounds — 38. New isoindigoide dyes from heterocyclic 2,3-diones — Synthesis and thermal rearrangement☆

Abstract The heterocyclic 2,3-diones 1 and 11 together with Lawesson reagent (LR) afford novel isoindigoide dyes 4 and 12 , respectively. 4a can thermally be isomerized into the pyrano[4,3-c]pyrane 6, accompanied by a significant hypsochromic shift which was corroborated by quantum chemical calculations. The phoshporanylidene derivative 13 was obtained via Wittig reaction of 1 . All structural assignments were based on X-ray studies of 4a and 13 .

Neat carbomethoxypivaloylketene—preparation and chemical reactivity

Abstract Neat carbomethoxypivaloylketene, the first fairly persistent α-oxoketene stabilized both electronically as well as sterically, is generated by flash vacuum pyrolysis of the corresponding furan-2,3-dione. It adds primary amines to afford pivaloyl-malonic acid amides and undergoes hetero-Diels–Alder reactions to furnish usual and unusual [4+2] adducts. Some stereo- and regiochemical features are verified with aid of 2D NMR experiments and a X-ray structure analysis.

Über Reaktionen mit cyclischen Oxalylverbindungen, 6. Mitt.: Synthesen von Heterocyclen, 161. Mitt.

Abstract4-Benzoyl-5-phenyl-2.3-dihydro-furan-2.3-dione (1) reacts with aryl isocyanates with loss of CO to give the oxazine-2.4-diones3,4, resp. However, the reaction between1 and p-tolylcarbodiimide goes further, yielding the 4-hydroxyquinoline9. The quinolines9 and17 are obtained by an independent route by heating the pyrrole-2.3-diones14 and15, which can be synthesized from dibenzoylmethane aniles and oxalyl chloride. α-Acylheterocumulenes (2,12,19, resp.) are postulated as intermediates for these cyclization reactions.Zusammenfassung4-Benzoyl-5-phenyl-2,3-dihydro-furan-2,3-dion (1) setzt sich mit Arylisocyanaten unter CO-Abspaltung zu den Oxazin-2,4-dionen3 bzw.4 um.1 und p-Tolylcarbodiimid reagieren hingegen zum 4-Hydroxy-chinolin9 weiter. Die 4-Hydroxy-chinoline9 bzw.17 erhält man unabhängig davon durch thermische Belastung der Pyrrol-2,3-dion-Derivate14 bzw.15, die aus den entsprechenden Dibenzoylmethananilen und Oxalylchlorid synthetisierbar sind. Als Zwischenstufen dieser Cyclisierungsreaktionen werden α-Acylheterocumulene (2 bzw.12,19) postuliert.

Imidoylketene - oxoketenimine rearrangement. Facile 1,3-shift of an alkoxy group

Thermal CO extrusion from 2,3-dihydropyrrole-2,3-dione 3 generates imidoylketene 4, which cyclizes to 2-methoxy-4-quinolone (6). Using flash vacuum pyrolysis and low temperature IR spectroscopy, it is shown that 4 interconverts with ketenimine 5 prior to cyclization to 6.

Synthesen von Heterocyclen, 158. Mitt@@@Syntheses of heterocycles, CLIV (reactions of cyclic oxalyl compounds, V): ber Reaktionen mit cyclischen Oxalylverbindungen, 5. Mitt.

Abstract4-Benzoyl-5-phenyl-2.3-dihydrofuran-2.3-dione (1) is converted at 120–140° under the loss of CO and CO2 to yield 3.5-dibenzoyl-2.6-diphenyl-4-pyrone (2, 79%). However, 3.7-dibenzoyl-4.8-diphenyl-1.5-dioxocin-2.6-dione (3) is formed in 90% yield, if1 is decomposed in boiling toluene in the presence of acids. The dibenzoyl ketene4 is postulated as the common intermediate.Zusammenfassung4-Benzoyl-5-phenyl-2.3-dihydrofuran-2.3-dion (1) wandelt sich beim Erhitzen auf 120–140° unter Abgabe von CO und CO2 in 3.5-Dibenzoyl-2.6-diphenyl-4-pyron (2, 79% d. Th.) um. Nimmt man die therm. Zers. in Toluol in Gegenwart katalyt. Mengen Säure vor, so bildet sich 3.7-Dibenzoyl-4.8-diphenyl-1.5-dioxocin-2.6-dion (3, 90% d. Th.). Als gemeinsame Zwischenstufe wird das Dibenzoyl-keten (4) postuliert.

Recent advances in ring transformations of five-membered heterocycles and their fused derivatives

Ring transformations of five-membered heterocycles and their benzologues for the recent 10 years are discussed and reviewed. These transformations are classified into four groups: (a) “classical ring transformations”, where the starting and resulting ring system is of the same size, but the heteroatoms and/or their positions have been changed; (b) “degenerate ring transformations”, where during the course of the transformation the starting compound and product have the same ring system, but the reaction proceeds by a ring opening and subsequent ring closure process; (c) “ring contractions” and “ring enlargements”, where the sizes of the product rings are smaller or larger, respectively, than those of the starting compound; and (d) “pseudo ring transformation” or “ring-chain transfer”, where the process is formally a ring transformation, but is realised by a ring closure of a side chain of the starting heterocycle and opening of the original ring. Reaction mechanisms of the most interesting ring transformations are also discussed.

Reactions of cyclic oxalyl compounds XXXIX. Reactions of 4-Ethoxycarbonyl-5-phenyl-2,3-dihydrofuran-2,3-dione with heterocumulenes andSchiff bases

SummaryFuran-2,3-dione1 reacts with arylisocyanates to the corresponding pyrrol-2,3-diones2, whereas conversion with diisopropylcarbodiimide affords the oxazepin-6,7-dione derivative3 in 68% yield. 1,3-Oxazines5,6, and7 were obtained by thermolysis of1 in boiling xylene in presence of arylisocyanates, diphenylketen-p-tolylimine, andSchiff bases, most likely by trapping the α-oxoketene intermediate4. Preparative flash vakuum pyrolysis (FVP) of1 and2b gave8 and9, respectively.ZusammenfassungDas Furan-2,3-dion1 reagiert mit Arylisocyanaten zu den entsprechenden Pyrrol-2,3-dionen, wohingegen mit Diisopropylcarbodiimid das 1,3-Oxazepinderivat3 in 68%iger Ausbeute gebildet wird. Die 1,3-Oxanzine5,6 und7 werden durch Thermolyse von1 in siedendem Xylol in Gegenwart von Arylisocyanaten, Diphenylketen-p-tolylimin undSchiffschen Basen erhalten, offensichtlich durch Abfangen des intermediär gebildeten α-Oxoketens4. Präparative Flash-Vakuum-Pyrolyse (FVP) von1 bzw.2b ergaben8 bzw.9.