Synthesis, Properties and Optical Resolution of rac-[n](1,6)Heptalenophanes

Abstract

[n](1,6)Heptalenophanes, rac-4a–c, having a five, six or seven membered methylene bridge, respectively, across the 12 π-perimeter were synthesized from rac-1,6-dimethylheptalene (1) in two steps. Detailed NMR and UV/vis studies of the new phanes reveal their bridged heptalene moiety to be more twisted than that of the parent heptalene system. Furthermore, the reduction of the [5](1,6)heptalenophane (4a) with lithium to its aromatic dianion 10 with 14 π-electrons is presented. NMR spectra of the latter show that its perimeter, although remarkable bent out-of-plane, still exhibits a considerable aromatic ring current. Liquid chromatography with triacetyl cellulose as stationary phase resulted in the optical resolution of racemic [5](1,6)heptalenophane (4a).