Atropisomerization in Confined Space; Cucurbiturils as Tools to Determine the Torsional Barrier of Substituted Biphenyls

The torsional barrier of biphenyls bearing a prochiral dimethylsulfonium group at their 3-position could be determined by variable-temperature H-1 NMR spectroscopy only after encapsulation into cucurbit[7]- or -[8]uril, which triggered the splitting of the two methyl signals. Confinement of the biphenyl units into the macrocycles amplifies the dissymmetry caused by the various ortho- and ortho-substituents and represents a new tool that can be used to access atropisomerization barriers of bi(hetero)aryl derivatives.