The Wittig reaction is a time-honored tool for transforming carbonyl groups into olefins, but it makes a waste product, triphenylphosphine oxide, that can be tough to remove. Now, Christopher J. O'Brien of the University of Texas, Arlington; Gregory A. Chass of the University of Wales, Bangor; and coworkers have found a way to greatly reduce that waste by developing a Wittig reaction that is catalytic in phosphine. The advance could benefit the performance of Wittig reactions on an industrial scale, where established ways of recycling triphenylphosphine oxide tend to be costly or impractical.
O'Brien's team uses diphenylsilane as a reducing agent to convert a cyclic relative of triphenylphosphine oxide, 3-methyl-1-phenylphospholane-1-oxide, to an active phosphine, which catalyzes the olefination and is then recycled (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200902525). This lets the team use catalytic amounts of phospholane, but there is a trade-off: The silane leaves behind a silanol by-product. The team is currently working on ways to recycle the silanol as well, O'Brien says.