Chemoselective Hydrogenation

I was intrigued by a report in Org Lett, 2009, 11, (13), 2722 by Kathlyn Parker et al where they describe a selective reduction of a propargylic alcohol in the presence of a vinyl halide, shown below.

They comment that vinyl iodides are generally considered incompatible with conditions usually associated with reduction of alkyne or alkene bonds.  The authors report screening a limited range of options (about 6) and were encouraged by the result with Crabtree’s iridium catalyst which resulted in complete reduction of the alkyne, leaving the vinyl iodide intact (90% yield).  They next looked at securing the desired reduction to obtain the allylic alcohol and found palladium over calcium carbonate in methanol showed promise, but with significant deiodination product.  Changing the solvent to hexane gave the required selective reduction in 86% yield.

Perhaps this system could find applications in other reduction situations where a halide need to be retained (eg where there is an aryl halide).