2-hydroxy-4-oxohex-2-enoic acid ethyl ester

2-hydroxy-4-oxo-hept-2-enoic acid ethyl ester

2-hydroxy-4-oxo-4-p-bromophenylbut-2-enoic acid ethyl ester

4-(2,4-bis(benzyloxy)-5-isopropylphenyl)-2-hydroxy-4-oxobut-2-enoic acid ethyl ester

(Z)-1-ethoxycarbonyl-3-oxo-3-pyridin-3-yl-propen-1-olate

ethyl 4-hydroxy-2-oxo-4-phenylbut-3-enoate

2-hydroxy-4-(2-hydroxy-4-methoxy-3,6-dimethyl-benzoyloxy)-3,6-dimethyl-benzoic acid ethyl ester