Aryl-substituted vic-dibromides

Aryl-substituted vic-dibromides undergo debromination to produce the corresponding E-alkenes when treated with indium metal in MeOH. Since debromination occurs by the usual trans-elimination, meso/erythro- and d,Z-/f/zreo-vic-dibromides would give trans- or cis-alkenes, respectively, as shown in Scheme 4.6. It is thus suggested that in this case the reaction occurs via a common relatively stable radical or anion intermediate, which directly collapses to -alkene. 

Indium is reported to be an efficient catalyst for the debromination processes of vic-dibromides. An illustration of the utility of this method is in the debromination of aryl-substituted vic-dibromides to produce the corresponding (E)-alkenes with indium metal in MeOH. In general, the reaction proceeds via a common, relatively stable radical intermediate, collapse of which leads directly to the (E)-alkenes, and methanol is found to be the best solvent for this reaction. ... 

Debromination. Aryl-substituted vic-dibromides (both meso and dl isomers) undergo debromination with indium in refluxing methanol to afford f j-alkenes. 

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