Dehalogenation regioselective

Selifonov SA, JE Gurst, LP Wackett (1995) Regioselective dioxygenation of ortfio-trifluoromethylbenzoate by Pseudomonas aeruginosa 142 evidence for 1,2-dioxygenation as a mechanism in orffio-halobenzoate dehalogenation. Biochem Biophys Res Comm 213 759-767. 

In all cases, the generation of a true nitrile imine was confirmed by the formation of the expected cycloadducts (e.g., 139) with the expected regioselectivity. However, in several cases, carbonyl derivatives (e.g., 137) were also formed in relatively low yield. These compounds were not formed when triethylamine was used as the base. From these data, it was suggested that the dehydrochlorination is a two-step process, involving first silver-ion promoted dehalogenation to give the carbocation... 

The use of phosphorus compounds has two advantages the reactions are performed in homogeneous mixtures and secondly, phosphorus derivatives are milder dehalogenation agents and, therefore, react with a better regioselectivity compared with most metallic agents, e.g. zinc.112... 

Ishii, A., Otsuka, T., Kume, K., et al. (2006) Regioselective preparation of 2-halo-2,3-dideoxy-3-fluoro-P-D-arabinofuranosyl nucleosides and their dehalogenation products. IP Patent 2006022009. 

The introduction of hydrogen or deuterium atoms into thiophenes is possible via the treatment of thienyUithiums with alcohols, water, deuterated alcohols, or deuterium oxide (Scheme 30) [24, 173, 174]. The combination of this method with a prior halogen-metal exchange reaction is a powerful tool for the regioselective partial dehalogenation of halogenated thiophenes [20, 174—190]. 

In the reaction of bromo benzene with ethylene trans-stilbene is formed as the target product. The formation of cis stilbene is not found within the detection limit of gas chromatography. The limitation of the molecular weight in the polyreaction is mainly caused by the dehalogenation of bromo benzene. By optimization of the reaction conditions (low reaction temperature, low catalyst concentration) the dehalogenation is pushed back below the detection limits of gas chromatography. The main defect structures in the polymer are caused by 1,1-disubstitution. This deHciency in the regioselectivity of Ae reaction can not be suppressed even by optimal reaction conditions. Therefore polyphenylene vinylene obtained by Ae Heck reaction has statistically a fold in Ae macromolecule after 30 - 100 monomer... 

---