Photochemical process for the synthesis of strobilurin

A process for the manufacture of synthetic strobilurin in the (E) configuration, which comprises condensing a correspondingly substituted cinnamaldehyde with 2-oxo-butyric acid in methanolic KOH to give the correspondingly substituted potassium salt of 3(Z), 5(E)-3-methyl-2-oxo-6-phenyl-3,5-hexadienic acid, converting this potassium salt with methanol/thionyl chloride to the corresponding methyl ester, converting the reaction product with methoxymethylene-triphenylphosphorane to 9(Z) strobilurin, and after chromatographic purification on silica gel irradiating the crude product by means of a mercury vapor lamp in acetone with addition of a small amount of benzene.