5-Aminoisoxazole-4-carboxylates, reaction with

Another group of reactions with the predominant cleavage of the ring comprises catalytic hydrogenation of isoxazole derivatives and has been investigated only recently. The most commonly used catalyst has been Raney nickel,but use has sometimes been made of platinum catalysts. Hydrogenolysis of the 0—N bond (172—>173) occurs in isoxazole, its homologs,and their functional derivatives, for example, isoxazole carboxylic acids- and 5-aminoisoxazoles. ... 

Thermal or photochemical treatment of isoxazoies 851 has been found to result in a ring-contraction reaction to produce acyl 277-azirines 852, which sometimes rearrange to form other heterocycles like oxazoles 853. This ring-contraction reaction can also be promoted by iron(ii) catalysts. Thus, 5-alkoxy- and 5-aminoisoxazoles isomerize to 27/-azirine-2-carboxylic esters and 2/7-azirine-2-carboxamides, respectively, in nearly quantitative yield by reaction with catalytic FeCb (Scheme 212) <1997T10911>. 

The reactions of the esters of 5-aminoisoxazole-4-carboxylic acids with acetic anhydride and aryl isocyanates yield substituted isoxazolo[5,4-J]pyrimidines 50 and 51 (86ACS(B)760, 86JHC1535) (Scheme 22). 

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