An unexpected bidirectional molecular rotor from unidirectional molecular motor via a stereoselective enamine-imine tautomerization process.

• Highly diastereoselective synthesis of molecualr rotor from molecualr motor. • First example of TGA on molecular motor. • Non-equilibrium vs equilibrium operation of molecular machines. Developing stereoselective synthetic method is very important to access chiral molecular devices. We herein demonstrate how a proton initiated stereoselective enamine-imine tautomerization converts a molecular motor into a simple rotor with high diastereoselectivity (>20:1 dr). NMR and X-ray crystallography were used to elucidate the structures of both the motor and rotor unambiguously. The activated motion of the rotor about its central single bond was studied from variable temperature NMR (293–423 K) and DFT calculations provide evidence of the origin of diastereoselectivity of enamine-imine tautomerization as well as the rotor dynamics with barrier as high as 39.3 kcal/mol. Results from our work may benefit future design towards stereocontrolled and adaptive molecular machines. [ABSTRACT FROM AUTHOR]