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 <b>6a</b> and <b>7a</b> as the initial prototypes are provided, and the synthesis of <b>6a</b> and <b>7a</b> and the separation of them from their atropisomers are detailed. The phosgene-powered unidirectional rotation of <b>6a</b> to its rotamer <b>6b</b> is demonstrated. It is further established that shortening the length of the tether (→<b>7a</b>) changes the rate-limiting step and accelerates the speed of rotation.