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).
Iodination of hydrazones
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.
Barton vinyl iodide synthesis
When iodine as an electrophile is replaced by aromatic selenyl bromides, the corresponding vinyl selenides are obtained:[4]
Vinyl selenide synthesis
^A new reaction of hydrazones Barton, D. H. R. , R. E. O'Brien and S. Sternhell Journal of the Chemical Society,1962, 470 - 476 doi:10.1039/JR9620000470 Abstract
^Studies on the oxidation of hydrazones with iodine and with phenylselenenyl bromide in the presence of strong organic bases; an improved procedure for the synthesis of vinyl iodides and phenyl-vinyl selenides Barton, D. H. R.; Bashiardes, G.; Fourrey, J.-L. Tetrahedron 1988, 44, 147 Abstract
^An improved preparation of vinyl iodides Derek H. R. Barton, George Bashiardes and Jean-Louis Fourrey Tetrahedron Letters Volume 24, Issue 15 , 1983, Pages 1605-1608 Abstract
^A new synthesis of phenylvinylselenides Derek H. R. Barton, George Bashiardes and Jean-Louis Fourrey Tetrahedron Letters Volume 25, Issue 12 , 1984, Pages 1287-1290 Abstract
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