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Hydrazone iodination is an organic reaction in which a hydrazone is converted into a vinyl iodide by reaction of iodine and a non-nucleophilic base such as DBU.[1][2] First published by Derek Barton in 1962 the reaction is sometimes referred to as the Barton reaction (although there are many different Barton reactions) or, more descriptively, as the Barton vinyl iodine procedure.
The reaction has earlier roots with the 1911 discovery by Wieland and Roseeu that the reaction of hydrazones with iodine alone (without base) results in the azine dimer (structure 2 in scheme 1).
In the original Barton publication[3] the reaction was optimized by using a strong guanidine base, the inverse addition of the hydrazone to an iodine solution, and by exclusion of water.
When iodine as an electrophile is replaced by aromatic selenyl bromides, the corresponding vinyl selenides are obtained:[4]