Stable salts unlock alternative to potentially explosive reagents in carbene chemistry
Many useful reactions in chemistry come with a trade-off: the reactive reagents that make them effective can also present practical and safety challenges. Carbene chemistry is one such example. For decades, chemists have relied on diazo compounds to generate reactive carbenes, even though diazoalkanes can be toxic, unstable and potentially explosive.
Stable salts have proven to be a safer alternative to potentially explosive reagents in carbene chemistry, according to a study published in Nature by researchers at the Max-Planck-Institut für Kohlenforschung. For decades, carbene chemistry has relied on diazo compounds, which can be toxic, unstable, and even explosive. However, the new approach involves bench-stable thianthrenium salts that serve as versatile precursors for carbene-transfer reactions.
This method overcomes a long-standing limitation in sulfonium-based carbene chemistry, as thianthrene's unusual electronic and steric properties make carbene transfer to metal more favorable. The researchers demonstrated this through cyclopropanation, a process that combines carbene fragments with a wide range of alkenes, including challenging internal, unactivated alkenes.
The use of these salts also avoids safety concerns associated with diazoalkanes, as they are readily prepared, bench-stable, and do not exhibit detectable exotherms during thermal analysis. Furthermore, the researchers demonstrated decagram-scale cyclopropanation using solvent-free ball milling, showcasing the practical and scalability advantages of this carbene chemistry.
The study establishes thianthrenium salts as a general platform for carbene-transfer chemistry, opening up the possibility of applying the same concept to a wider range of carbene-mediated transformations in the future.
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