at 10 u00b0 c the resulting precipitate is filtered and crystallized from acetonitrile to obtain the hemi e 2 butenedioate salt mp 128 u00b0 130 u00b0 c of the title compound in the same manner but replacing 4 5 dihydro 5 methyl 4 oxo 5 phenylfuran 2 carboxylic acid with an equivalent amount of another compound of formula i described in example 4 the following compounds of formula i are obtained respectively 4 5 dihydro 5 1 methylethyl 4 oxo 5 phenylfuran 2 carboxylic acid 3 pyridinylmethyl ester 5 4 chlorophenyl 4 5 dihydro 5 methyl 4 oxofuran 2 carboxylic acid 3 pyridinylmethyl ester nmr cdcl 3 u03b41 77 s 5 46 s 6 29 s 7 42 m 7 86 m and 8 70 m 4 5 dihydro 5 5 dimethyl 4 oxofuran 2 carboxylic acid 3 pyridinylmethyl ester mp 109 u00b0 110 u00b0 c spiro furan 5 4h 1 39 2 39 h naphthalene 3 39 4 39 dihydro 4 oxo 2 carboxylic acid 3 pyridinylmethyl ester 5 butyl 5 ethyl 4 5 dihydro 4 oxofuran 2 carboxylic acid 3 pyridinylmethyl ester 4 5 dihydro 4 oxo 5 5 diphenylfuran 2 carboxylic acid 3 pyridinylmethyl ester 5 cyclohexyl 4 5 dihydro 4 oxo 5 propylfuran 2 carboxylic acid 3 pyridinylmethyl ester 4 5 dihydro 5 ethoxymethyl 5 3 methoxyphenyl 4 oxofuran 2 carboxylic acid 3 pyridinylmethyl ester 4 5 dihydro 5 3 4 diethylphenyl 5 4 nitrophenyl 4 oxofuran 2 carboxylic acid 3 pyridinylmethyl ester 1 7 dioxaspiro 4 4 non.