Synthesis of 1,2-dibromoalkenes

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Stereoselective halogenations of alkenes and alkynes can be conducted in room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium chloride as "green" recyclable alternatives to chlorinated solvents.
C. Chiappe, D. Capraro, V. Conte, D. Pieraccini, Org. Lett., 2001, 3, 1061-1063.

Tetrapropylammonium nonabromide (Pr₄NBr₉) is a solid reagent for rapid bromination reactions of various substrates. The reagent exhibits reactivity similar to that of elemental bromine, but shows higher selectivity and it is easier and safer to store and to handle.
T. M. Beck, H. Haller, J. Streuff, S. Riedel, Synthesis, 2014, 46, 740-747.

Copper(II) bromide as both the reacting partner and the catalyst enables a highly stereoselective and efficient dibromination of alkynes to yield (E)-dibromoalkenes. The reaction conditions are exceptionally mild, and a wide range of functional groups are well tolerated.
J. Xiang, R. Yuan, R. Wang, N. Yi, L. Lu, H. Zou, W. He, J. Org. Chem., 2014, 79, 11378-11382.

Unsaturated compounds such as alkenes, alkynes, allenes, and methylenecyclopropanes (MCPs) can be dibrominated within minutes by NBS and lithium bromide in THF at room temperature in good to excellent yields under mild conditions.
L.-X. Shao, M. Shi, Synlett, 2006, 1269-1271.