The Wittig reaction was discovered by Georg Wittig and co-workers in 1953 and for which Wittig was awarded the chemistry Nobel Prize in 1979. Since its discovery, the Wittig reaction has probably been the preferred choice of synthetic chemists towards the synthesis of alkenes. The formation of the alkene proceeds through the reaction of an aldehyde or ketone with a phosphonium ylide. The success of the reaction is due first to its regioselectivity, as the double bond of the alkenes is formed only between the reacting carbon of the ylide and the carbonylic partner, and second to its stereoselectivity to the formation of one of the two possible geometric isomers. The major drawback of the reaction is the generation of stoichiometric amounts of undesired triphenylphosphine oxide, a byproduct that frequently complicates the purification of the desired product.
In a very smart approach to overcome the problem of generating such a big amount of phosphine oxide waste, O’Brien and co-workers from the University of Texas designed a catalytic version of the Wittig reaction. The challenges: to generate in situ the reactive ylide and to reduce the phosphine oxide without reducing the carbonyl compounds involved in the reaction. The solution: the utilization of a cyclic phosphine that is reduced by Ph2SiH2, a reducing agent mild enough to leave the carbonyl coupling partners intact. The catalytic version has proved effective with a series of aldehydes and stabilised or semi-stabilised ylides. The reaction represents an important first step to a general catalytic Wittig reaction and more research will be needed to achieve the same degree of effectiveness as the stoichiometric variant in terms of the scope of substrates and regioselectivity.
Do you want to know more? Take a look to the original paper:
Christopher J. OBrien, Jennifer L. Tellez, Zachary S. Nixon, Lauren J. Kang, Andra L. Carter, Stephen R. Kunkel, Katherine C. Przeworski, and Gregory A. Chass. Recycling the Waste: The Development of a Catalytic Wittig Reaction. Angew. Chem. Int. Ed. 2009, 48, 6836 –6839.