| 摘要 |
A method for the preparation of a compound of formula (II) wherein R1 and R2 are independently H, alkyl, alkoxy, oxoalkyl, alkenyl, aryl or arylalkyl whether unsubstituted or substituted, optionally interrupted by one or more hetero atoms, straight chain or branched chain, hydrophilic, hydrophobic or fluorophilic; R3, R4, R5 and R6 are independently or all hydrogen or halogen; provided that at least two of the R3, R4, R5 and R6 are halogens.
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