Synthesis and Structure of Optically Active 1,12-Diethyl- and 1,12-Diisopropylbenzo[<i>c</i>]phenanthrenes: An Isopropyl Group Can Be Smaller than a Methyl Group

Abstract

Abstract 1,12-Diethyl- and 1,12-diisopropylbenzo[c]phenanthrene-5,8-dicarboxylic acids were synthesized, and resolved. The dihedral angles formed by the A and D rings increased in the order of diisopropyl &amp;lt; diethyl &amp;lt; dimethyl as indicated by X-ray analysis, which showed that the strain decreased with the increase of the bulkiness at the 1,12-groups.