means a hydrogen atom or an alkyl, aryl or aralkyl group, and X denotesa hydroxyl group or an eliminative substituent easily reactable with a hydroxyimino group.Illustrative of the eliminative group (X) easily reactable with a hydroxyimino group include cyano group, halogen atoms such as C.sub.1 and Br, p-nitrophenoxy group, and those represented by the formula ##STR10## wherein R.sub.6 means an