The leaves of the common guava plant Psidium guajava have long been used as an herbal remedy. Natural products extracted from these leaves include (+)-psiguadial B, which is toxic to liver cancer cells. (+)-Psiguadial B possesses the kind of structure that makes synthetic chemists swoon. It’s loaded with strained rings and stereocenters—perfect for trying out some new chemistry. Caltech chemists led by Sarah E. Reisman now report the first enantioselective total synthesis of (+)-psiguadial B (J. Am. Chem Soc. 2016, DOI: 10.1021/jacs.6b07229). The chemists completed the synthesis in just 15 steps, starting from a simple diazoketone. Reisman’s group first set out to make the strained portion of the molecule, which includes a fused trans-cyclobutane ring. A key transformation they developed en route was a tandem reaction combining a Wolff rearrangement and an asymmetric ketene addition—the first time this combo has been reported. This step creates the cyclobutane portion of the molecule while incorporating an important directing group for a subsequent C–H functionalization reaction. The chemists hope they can use this strategy to make other molecules with trans-cyclobutane rings.