8,8′-Dialkyl-1,1′-biisoquinolines: preparation, absolute configuration and unexpected racemization behaviour †

A series of 8,8′-dialkyl-1,1′-biisoquinolines, in which methyl, ethyl and isopropyl groups are introduced for enhancing the transannular steric hindrance, are synthesized. The atropisomeric biisoquinolines are separated into both enantiomers, of which the absolute configurations and the optical stabilities are determined. Contrary to prior expectations, the racemization behaviour is inversely proportional to the steric size of the alkyl groups.