Santa Jansone-Popova and Jeremy May, University of Houston, Texas, USA, explain how they can build a common structural motif, bridged bicycles, found in many natural products including carnosol and platencin. They use a carbene cascade reaction to modify alkynyl diazoesters, which themselves are readily derived from cyclic ketones.

The reaction proceeds, first, through rhodium-catalyzed diazo decomposition, followed by carbene/alkyne metathesis, and finally a C–H bond insertion process. The result is that the team can make a strained bridged bicycle in a single reaction scheme with the formation of multiple C–C bonds.

Given that many of the natural products containing such a moiety have biological activities including acting as antioxidants, anticancer, and antibacterial agents, novel routes to their synthesis and the formation of analogs could be useful in medicinal chemistry.

• Synthesis of Bridged Polycyclic Ring Systems via Carbene Cascades Terminating in C–H Bond Insertion,
  Santa Jansone-Popova, Jeremy A. May,
  J. Am. Chem. Soc. 2012.
  DOI: 10.1021/ja308305z