Molecular Motors: A Tour de Force

Significance

In what is described as the author’s final contribution to molecular motors, this article describes the synthetic challenges and practical difficulties faced in their epic quest for a continuously rotating molecular motor. The authors had previously demonstrated unidirectional rotary motion (T. R. Kelly, H. De Silva, R. A. Silva Nature 1999, 401, 150-152). The amino-functionalized triptycene framework is formed via a nitrobenzyne cycloaddition to an anthracene derivative to give a mixture of separable regioisomers. The helical arm is then constructed through a standard Wittig reaction followed by a stilbene photocyclization. Although numerous functional groups were tested in the photocyclization, including the desired di­methylaminopyridine, each produced lower yields than the chloro substituent (26% yield). Finally, the Stille coupling proved challenging as well, with an optimized yield of 16%.