prov:value
| - To prepare the compounds of the formula I.1, in which R1, R2, R3 and R4 are as defined above, which are used according to the present invention, it is possible, for example, to reduce a 1,8-dihalogen-substituted anthraquinone of the formula III, in which Ya and Yb have one of the above meanings and are, for example, halogen, in particular chlorine or bromine, according to scheme 1 below to give a
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