Untersuchungen an 1,3‐Dicarbonyl‐Verbindungen, 21. Mitt. 3‐Acyl‐4,5‐dihydro‐4‐oxo‐indeno[1,2‐b]pyrane

Abstract

Es wird uber die Darstellung und Reaktionen des Aldehyds 3 und des Nitrils 11 berichtet. l,3-Diearbonyl Compounds, XXI: 3-Acyl-4,5-dihydroindeno[l,Z-b]pyran-4-onesThe synthesis and the reactions of the aldehyde 3 and the nitrile 11 are reported. Erhitzt man alternativ zum erstgenannten Verfahren 3 in Ameisensaure mit Natriumformiat und Hydroxylamin-HCI'), SO wurden durch fraktionierte Kristallisation drei Produkte isoliert; 6, dessen Oxim 9 und erstmals das gewiinschte Nitril 11. Aufgrund dieser Ergebnisse war es zweckmaBig, 3 zuerst unter sauren Reaktionsbedingungen in das Oxim 7 zu uberfiihren. Dann wurde die Dehydratisierung zum Nitrilll optimiert. Die Reaktion von 7 rnit Carbonyldiimidazol ergab ein trennbares Gemisch, bestehend aus 6 und 11; rnit Trifluoracetylimidazol konnte 1 1 rein und mit bester Ausbeute isoliert werden.

β-Oxidation of α,β-Unsaturated Carbonyl Compounds

“…The amino oxime was also formed as a side product in 10% yield. 168 Nitrosobenzene oxidizes the b-carbon of methylidenemalonate and produces a product equivalent to that obtained from reaction of hydroxymethylene malonate with N-phenyl-hydroxylamine (Scheme 101). 169…”

A Rare Acid-Promoted Elimination of O-Methyl Oximes: A Practical Synthesis of 3-Cyano-4-benzopyrones

“…We began our synthesis of 3-cyano-benzopyrones by focusing on a few reported procedures describing preparations from the corresponding aldehydes through oxime intermediates . As shown in Scheme , when 3-formyl-4-benzopyrone 5 is refluxed with H 2 NOH−HCl and a catalytic amount of concentrated HCl in 95% EtOH, the corresponding oxime 6 should be formed and undergo facile dehydration to provide 3-cyano-4-benzopyrone 8 .…”

“…The isoxazole 7 has been reported but only as a minor product, and given the aromatic nature of isoxazole, its formation could be readily rationalized as shown in Scheme . Nevertheless, as suggested by the reported procedures,15a these isoxazoles ( 7 ) were heated in DMSO at 85 °C in an attempt to crack open the aromatic isoxazole ring and force the reaction pathway towards the desired 3-cyano-4-benzopyrones ( 8 ). These efforts also failed in leading to the desired 3-cyano-4-benzopyrones ( 8 ) in significant yields after taxing chromatographic purifications.…”

“…Given this preparation of 3-cyano-4-benzopyrones from 3-formyl-4-benzopyrones via the corresponding O -methyl oxime derivatives, it is then possible to construct many 3-cyano-4-benzopyrones with various substitution patterns on the aromatic ring because the starting 3-formyl-4-benzopyrones can be readily prepared from available hydroxyacetophenones 15b. As shown in Scheme , the starting 2‘-hydroxy-1‘-acetonaphthone could be converted into the 3-formyl-4-naphthopyrone 29 in 96% yield under the Vilsmeier conditions.…”