Chemists have created a new class of diene reagents that enable back-to-back cycloaddition reactions all in one operation. The development could help shorten the synthesis of polycyclic natural products and imaging agents while saving time, cutting cost, and reducing waste (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b04091). Stanford University’s Paul A. Wender and colleagues came up with the reagent after pondering how nature often achieves chemical complexity through recursive processes—that is, serially repeating a bond-forming event. They decided to try that approach to amplify the synthetic utility of already-useful Diels-Alder and metal-catalyzed cycloaddition reactions. Using the hard-to-prepare and short-lived tetramethyleneethane (TME) diradical as a model, Wender’s team designed 2,3-dimethylene-4-trimethylsilylbutan-1-ol, known as DMTB. This TME equivalent reacts with a variety of dienophiles in an initial cycloaddition, triggering an elimination step that generates a new diene for a second cycloaddition. The Stanford group has used DMTB to carry out a range of consecutive Diels-Alder and metal-catalyzed cycloadditions. In one example, the researchers used it in the synthesis of a new solvatochromic dye, called 6-DMA, which they expect to be a valuable on-off fluorescence probe for studying biological systems.