5-phenyl-4-oxazolecarboxylic acid methyl ester

Duarte and co-workers correctly identified the product from the Michael addition of benzohydroxamic acid to a propiolate ester to be a 1,4,2-dioxazole 1626, not an oxaziridine 1627 (Scheme 1.417). The authors converted 1626 to a mixture of (E/Z) lactoxime (9-vinylether sodium salts 1628, from which 2-phenyl-4-oxazolecarboxylic acid methyl ester was isolated upon thermolysis. 

Unlike ynamines, ethyl vinyl ether requires the more electron-deficient 4-nitro-2-phenyl-5-oxazolecarboxylic acid methyl ester 271b for reaction to occur. The initial [4 + 2] cycloadduct 279 undergoes further reaction with ethyl vinyl ether to give the tricyclic oxazoline 280 in 76% yield (Scheme 8.79). 

In a model study, Helquist and co-workers described the reaction of dimethyl diazomalonate 128 with benzonitrile to prepare 5-methoxy-2-phenyl-4-oxazolecar-boxylic acid methyl ester 129 nearly quantitatively (Scheme 1.35). Several other 2-aryl-5-methoxy-4-oxazolecarboxylic acid methyl esters were prepared analogously. In addition, 2-aIkyl(aIkenyl)-5-methoxy-4-oxazolecarboxylic acid methyl esters were also prepared, although the yields for aliphatic nitriles were not as good, unless the nitrile was used as solvent. Other metal salts—including Rh2 (NHAc)4, Cu(OTf)2, Cu(C2Hs-acac)2, Rh2(02CC3H7)4, and Rh3(CO)ie— were not as effective as Rh2(OAc)4 in this reaction. 

RHODIUM-CATALYZED HETEROCYCLOADOITION OF A DIAZOMALONATE AND A NITRILE SYNTHESIS OF 4-CARBOMETHOXY-5-METHOXY-2-PHENYL-1,3-OX AZOLE (4-Oxazolecarboxylic acid, 5-methoxy-2-phenyl-, methyl ester)... 

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See also in sourсe #XX -- [ , ]

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