Hydrazone iodination
Hydrazone iodination is an
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
Reaction mechanism
The reaction mechanism proposed in the original Barton publication is outlined as follows:
The hydrazone is
This reaction is related to the Shapiro reaction.
Scope
An example of this procedure is the reaction of 2,2,6-trimethylcyclohexanone to the hydrazone by reaction with hydrazine and triethylamine in ethanol at reflux followed by reaction of the hydrazone with iodine in the presence of 2-tert-butyl-1,1,3,3-tetramethylguanidine (cheaper than DBU) in diethyl ether at room temperature.[5] Another example can be found in the Danishefsky Taxol total synthesis.
In one study
References
- ^ 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
- ^ Preparation and reactions of 2-tert-butyl-1,1,3,3-tetramethylguanidine: 2,2,6-trimethylcyclohexen-1-yl iodide Derek H. R. Barton, Mi Chen, Joseph Cs. Jászberényi, and Dennis K. Taylor Organic Syntheses, Coll. Vol. 9, p.147 (1998); Vol. 74, p.101 (1997) Article Archived 2005-11-17 at the Wayback Machine
- Chemical Communications, 2006, 1831 - 1832 Abstract