Halogenation chiral starting material

Still, there remain many open problems. It would be efficient to be able to prenylate or ferf-prenylate indole regioselectively at the benzene positions 4, 5 and 6 without having to rely on pre-functionalisation such as halogenation or hydroxylation. Here, deeper investigation of prenyl shifts and of CH functionalisation on indole is required. Enantioselective catalysis has to be explored further towards the synthesis of optically pure 3-prenylated or -tert-prenylated alkaloids. A chiral version of NBS would be helpful. In the case of conformationally flexible starting materials, the diastereoselectivity of oxidative cyclisations of tryptophan-derived diketopiperazines is still not convincing. In the area of chemoenzymatic synthesis, the number and availability of enzymes has to be enhanced and their substrate tolerance has to be elucidated in more detail. 

When a halogenation reaction takes place at a chirality center, a racemic mixture is obtained regardless of the configuration of the starting material. 

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