Configurationally stable axially chiral N,N’-dialkyl-2,2’-biphenylene-N,N’-ureas

The configurational stability of compounds 1–4 has been confirmed by NMR spectroscopy and chiral chromatography (analytical separation of enantiomers 1 and 2); the antiaromatic (4n) destabilisation of the planar transition state of enantiomerisation is discussed.