Chemists build a triple norbornane

As molecular explorers, chemists often venture out into “chemical space” to see what strange new discoveries they can make. To assist in these efforts, researchers have devised algorithms that take a prescribed set of elements and number of atoms and work through all the possible combinations leading to stable molecules that are synthetically feasible. Using the GDB-11 database, which constructs molecules containing C, N, O, or F and containing up to 11 framework atoms, a team led by Marcel Mayor of the University of Basel decided to zoom in on polycyclic hydrocarbons lacking three- or four-membered rings. This structural motif is sometimes found in natural products that have potential as drug candidates. Among the 124 molecules that popped up in the database search, only three had no real-world counterparts. One of these compounds, an intricate symmetrical saturated C₁₁H₁₆ molecule, was “particularly appealing and eye catching,” so the researchers decided to try to make it (Chem. Commun. 2017, DOI: 10.1039/c7cc06273g). The compound’s scaffold consists of two norbornane units that share a pair of neighboring edges, an arrangement that coincidentally results in a third norbornane subunit. Using a total synthesis strategy similar to the way chemists go about preparing natural products, the researchers succeeded in making a racemic mixture of the chiral compound, which they have named trinorbornane, in nine steps with 7% overall yield.