A powerful but straightforward method for olefin cross-coupling enables synthesis of compounds previously impractical or even impossible to make, claim its developers at the Scripps Research Institute, La Jolla, Calif. The technique allows construction of highly substituted and uniquely functionalized carbon-carbon (C-C) bonds with unprecedented ease, they add. The method uses a simple iron catalyst, a commercially available silane and ethanol as solvent, and operates at ambient conditions.
Figure 1. Group has developed new method for olefin cross-coupling. Source: Scripps Research Institute.
“We expect that this method will have immediate application to pharmaceuticals, materials, and even agricultural and fragrance chemistry,” says Phil Baran, a professor in the chemistry department at the Institute. “Any compound that bears fully substituted sp3 carbon atoms would be an ideal candidate,” adds Julian Lo, a graduate student who is a member of the research team.
“This new chemistry allows for bond constructions that have previously been simply unimaginable,” Baran contends. The team has made more than 60 compounds using the method. “Around 90% of these are new chemical entities,” he notes. “Functional groups that would be destroyed by other cross-coupling methods are totally unscathed when using our method,” adds Lo. The team hopes to run the reaction on a larger, multigram, scale in the near future. More details on the method appear in a recent article in the journal Nature.
“We are rewriting the rules for how one thinks about the reactivity of basic organic building blocks and in doing so we’re allowing chemists to venture where none has gone before,” Baran believes. “Our method can bring into reality the type of molecules that have only existed on paper or as part of thought experiments. The only limitation of our method is our own imaginations,” says Lo.
The researchers are interested in refining the reaction both to create new chemical entities and to improve its stereo-specificity. “Additionally, we’re looking at expanding the mode of reactivity of this Fe-based catalysis,” notes Lo.
The method does pose some challenges that need addressing, admits Lo. These include regiochemical issues with some of the more-esoteric donor olefin classes, i.e., vinyl boranes and silanes. In addition, reducing the amount of acceptor olefin required from the three-fold excess now typically necessary would be beneficial.