A Rationally Designed Prototype of a Molecular Motor.

A proof of principle of the first rationally designed, chemically powered, molecular-scale motor is described. The thermodynamic considerations leading to the choice of 6a and 7a as the initial prototypes are provided, and the synthesis of 6a and 7a and the separation of them from their atropisomers are detailed. The phosgene-powered unidirectional rotation of 6a to its rotamer 6b is demonstrated. It is further established that shortening the length of the tether (→7a) changes the rate-limiting step and accelerates the speed of rotation.