General procedure for isoxazole-imidazole interconversion

4-Aminoisoxazole hydrochloride (1.33 g, 11 mmol) is refluxed (24 h) in a mixnire of formic acid (11ml) and ethyl formate (110 ml). After concentration of the mixture in vacuo the resulting oil is diluted with toluene and re-evaporated to give a dark tan solid. Flash chromatography [34] (MeOH-CHCl3, 5 95) gives the product (1.09g, 89%), m.p. 125-129°C. Further purification can be achieved by recrystallization from cyclohexane-ethyl acetate. 

This is made from A -(4-isoxazolyl)formamide by the above general procedure with the modification that the intermediate a-amino-a,j8-unsaturated aldehyde (7) (R, = H) precipitates. In consequence, the catalyst is not filtered 

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