Look, no ortho substituents! A series of polycycles were prepared by using a three-component Joulli  -Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a @entity15060 ring with no ortho substituents was measured, and was highly dependent on the substitution. Rotamer half-lives of up to 21 h at 298 K were observed (see figure). Rotamers resulting from this @entity717 were isolated for the first time.A series of polycycles was prepared by using a three-component Joulli  -Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a @entity15060 ring with no ortho substituents was measured by using, in general, variable-temperature HPLC. The rate of rotation was highly dependent on substitution and rotamer half-lives of up to 21 h at 298 K were observed. Insights into the effect of substitution on the rate of rotation were gleaned through electronic structure calculations on closely related derivatives. Rotamers resulting from @entity717 about a bond between an sp(3)-hybridised @entity505 atom and a @entity15060 ring with no ortho substituents were isolated for the first time, and the equilibration of the separated rotamers was followed by using analytical HPLC. It was demonstrated, for the first time, that a highly hindered environment for the sp(3)-hybridised atom is sufficient for @entity717 about a single bond between sp(3)- and sp(2)-hybridised @entity505 atoms.

Remarkably XXXX about a single bond between an sp(3)-hybridised @entity505 atom and an aromatic ring without ortho substituents.

@entity505 :: ('MESH:D002244', 'Chemical') :: ['carbon'] @entity717 :: ('MESH:D009069', 'Disease') :: ['restricted rotation', 'slow bond rotation'] @entity15060 :: ('CHEBI:30396', 'Chemical') :: ['phenyl']
@entity717 :: (MESH:D009069,Disease) :: ['slow rotation']
