Azlactones alkylidene

Wie eine genauere Untersuchung der Bergmann-Stemschen Azlacton-Synthese zeigte, hangt die Struktur der entstehenden Alkyliden-oxazoli-... 

The Erlenmeyer amino acid synthesis962 depends on condensation of an aldehyde with hippuric acid this gives an alkylidene azlactone, which is an intermediate in the synthesis, being converted into an <%-amino acid by reduction and hydrolysis. 

The alkylidene azlactones are prepared by boiling hippuric acid, the aldehyde, glacial acetic acid, and sodium acetate under reflux. As a class they are amenable to many types of reaction by hydrolysis with alkali they afford oc-oxo acids, and on oxidation by hydrogen peroxide in alkali they yields the... 

Mit aromatischen, aber auch aliphatischen (vgl. S. 506 f.) Aldehyden, mit Ketonen und Acetalen kondensiert es unter der Katalyse organischer Basen (z. B. Piperidin, Morpholin) leicht zu den entsprechend substituierten 4-Aralkyliden- und 4-Alkyliden-Derivaten (60-90% Ausbeute)96-98. Letztere lassen sich, wie die ungesattigten Azlactone, durch Reduktion und alkalische Hydrolyse oder direkt mit rotem Phosphor/Jodwasserstoffsaure in a-Amino-carbonsauren uberfuhren (65-90% Ausbeute)96 98 ... 

Conversion of azlactones to other heterocyclics 1,2,4-Triazines from 4-alkylidene-5-oxazolones... 

P,P-Disubstituted alkylidene derivatives of oxindole, azlactone, and y-butyrolactone are used as precursors of vinylogous enolates, which are highly stabilized owing to the heteroaromatic nature of the enolate components. Although these a,p-unsaturated carbonyl systems can act as electrophilic Michael acceptors, the presence of two p-substituents seems to suppress nucleophilic attack on the P-carbon. 

For instance, N-benzoyl glycine (26, hippuric acid) can be transformed to a 4-alkylidene azlactone (27) by treatment of 26 and an aldehyde (a) with Ac20/Na0Ac via intermediate formation of the azlactone 25 and (b) with polyp hosphoric acid via intermediate formation of alkylidene hippuric acid (28). Under the conditions of (b), ketones can be used in the Erlenmeyer synthesis. 

Catalytic hydrogenation of the 4-alkylidene azlactones 27 affords the 4-alkyloxazolones 29, whose hydrolysis in acid medium renders amino acids 30 (formally a-alkylated glycines) and benzoic acid ... 

Saturated azlactones are colorless liquids or low-melting solids. Unsaturated azlactones are solids, often high-melting, and the majority have colors tanging from Ught yellow th dark red. The color, is most intense in 2-aryl-4-aralkylidene-5-oxazolones the 2-alkyl-4-alkylidene-5-oxazolones are colorless. 

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