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 i sopropyl groups are introduced for enhancing the transannular steric hindra nce, are synthesized. The atropisomeric biisoquinolines are separated into both enantiomers, of which the absolute configurations and the optical stab ilities are determined. Contrary to prior expectations, the racemization be haviour is inversely proportional to the steric size of the alkyl groups.