[(5-Hydroxy-4-oxo-2,5,7-cycloheptatrien-1-yl)amino]oxo-acetic acid ethyl ester 、
[(3-hydroxy-2-oxo-3,5,7-cycloheptatrien-1-yl)amino]oxo-acetic acid ethyl ester 以[(3-methoxy-2-oxo-3,5,7-cycloheptatrien-1-yl)amino]oxo-acetic acid methyl ester is obtained的产率得到[(3-methoxy-2-oxo-3,5,7-cycloheptatrien-1-yl)amino]oxo-acetic acid methyl ester