Breaking the Unbreakable: Chalcogen Bonding Tackles Sigma Bonds

In the bustling marketplace of organic chemistry, chalcogen bonding has recently set up shop as a versatile platform for catalysis. Until now, however, it has been somewhat selective, preferring to mingle with lone pairs and pi electrons while giving the cold shoulder to sigma electrons. A new study changes this narrative entirely, demonstrating that chalcogen bonding can indeed crack the stubborn carbon-carbon (C-C) sigma bond of [1.1.1]propellane.

This is no small feat. Conventionally, chemists rely on heavy-hitting transition metals to activate these bonds. Yet, in the specific pursuit of constructing spiro[3.3]heptanes—distinctive molecular structures comprising two rings joined at a single atom—those metal catalysts proved ineffective when attempting to bridge propellane with cyclopropenones. The researchers discovered that a main-group chalcogen catalyst could succeed where metals failed. It operates via a 'dual catalysis mode', not only activating the propellane but also stabilising the fleeting alkyl carbene intermediate.

The efficiency of this method is striking. Reactions that might otherwise require harsh conditions are completed within minutes at room temperature, using a mere 2.5 mol per cent of the catalyst. This breakthrough suggests that main-group elements can orchestrate complex insertions previously deemed elusive, proving that in synthesis, a precise touch often outperforms brute force.