4- Acylamino-oxazolinones

Although imidazolinones are usually resistant to hydrolysis, oxazolinone rings are often easily opened. In acid-catalyzed reactions of this type, water converts azlactones (181) into a-acylamino-a,/3-uhsaturated acids (182) (77AHC(21)175). 1,3,4-Oxadiazolinones are readily opened by hot water to give hydrazine carboxylic acids which undergo decarboxylation. 

Auch durch Zusatz von Lewis-Sauren wird die Reaktionsfahigkeit der Carbonylgruppe stark erhoht. So liefem Az-Oxazolinone mit Aromaten und AICI3 hohe Ausbeuten an aromatischen a-Acylamino-ketonen (34,36,... 

Mit Grignard-Verbindungen reagieren A2-Oxazolinone nach erfolgter Ringoffnung weiter, wobei tert. a-Acylamino-alkohole (31) entste-hen 9,12,48,131). 

Besonders glatt reagieren die A3-Oxazolinone 5 mit Aminen in Alko-holen, wobei 2-Alkyl(Aryl)amino-2-acylamino-carbonsaure-ester 73 (Y = NR4R5, Y = OR ) erhalten werden ( ) Vgl. auch 1.110,iso)). Analog ergeben Aminosaureester in Alkoholen Verbindungen vom Typ 75 119,120,146)... 

Verwendet man zur Acylierung Carbonsaureanhydridc/Py ridi n, so besteht die Gefahr, daB das 4-Acyl-oxazolinon zum a-Acylamino-keton gespalten wird (Dakin-West-Reaktion) 96>. So liefern die 4-Acyl-oxazoli-none beim Erwarmen mit Eisessig/Pyridin (96> vgl. auch 171)) oder was-serfreier Oxalsaure in guten Ausbeuten a-Acylamino-ketone. 

A Dakin-West reaction on plant scale is demonstrated by elaboration of a modified procedure avoiding uncontrolled release of carbon dioxide. It seems to be generally accepted that the mechanism involves dehydrative formation of an azlactone (oxazolinone), which is then C-acylated (in equilibria with G-acylation), undergoes ring-opening hydrolysis, and then decarboxylates to form the acylamino ketone. Pyrimidine ring formation is achieved in a simple one-pot reaction, which is followed by a simple isomerization. Laboratory experiments had made clear that the mechanism... 

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