Weinreb Amide as Secondary Station for the Dibenzo-24-crown-8 in a Molecular Shuttle

Here is reported the synthesis of a new molecular shuttle: it consists of a dibenzo-24-crown-8 (DB24C8) that surrounds a molecular axle containing an ammonium group and a newly considered Weinreb amide as stations. At the protonated state the DB24C8 is localized around the best ammonium station, while deprotonation-carbamoylation of the ammonium triggers the shuttling of the macrocycle around the Weinreb amide site. Further post-interlocking modification of the [2]rotaxane was attempted through the cleavage of the Weinreb amide bond using a Grignard reagent. While the non-interlocked molecular axle was cleaved after a short time in mild conditions, the Weinreb amide bond remained unaltered in the [2]rotaxane species over time, even in the presence of a larger amount of Grignard and at a higher temperature, highlighting the protection shield of the macrocycle around the encircled axle.