摘要 |
This invention relates to compounds having the formula <IMAGE> wherein R1 represents hydrogen, halogen or alkoxy, R2 and R3 are hydrogen, alkanoyl or alkyl each being the same or different, R4 represents alkanoyloxyalkyl, hydroxyalkyl, hydrogen, alkyl, alkoxyalkyl, alkenyl, alkynyl, adamantanecarbonyloxyalkyl, bromoalkyl or benzoyloxyalkyl.
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