Multiply bridgehead- and periphery-substituted tribenzotriquinacenes—highly versatile rigid molecular building blocks with C3v or C3 symmetry

The chemical versatility of tribenzotriquinacenes as building blocks bearing rigid carbon frameworks with convex/concave molecular surfaces is presented. As revealed by X-ray single crystal structure analysis of the centro-methyl derivative, the tribenzotriquinacene skeleton adopts a perfect C3v symmetrical conformation in the solid state. Within the crystal, the molecules are strictly aligned in stacks along the C3v molecular axis of symmetry, at a distance of 6.0 Å and with zero mutual turn along the axis. Bromination of the three benzhydrylic bridgeheads of the parent tribenzotriquinacene, of its centro-methyl homologue, in particular, and of its centro-ethyl homologue has opened a convenient access to a large variety of three-fold substituted or functionalized derivatives with C3v or C3 molecular symmetry. Thus, several 1,4,7,10-tetrasubstituted tribenzotriquinacenes have become accessible bearing three hydrocarbon or heteroatomic groups in strictly eclipsed orientation with respect to the central substituent. A number of mono- and difunctionalized methyltribenzotriquinacenes have also been prepared. The potential of directed functionalization of the six peripheral positions of the aromatic rings, and of both the three benzhydrylic bridgeheads and the six peripheral positions of the tribenzotriquinacene framework is demonstrated with 1,4,7,10-tetramethyltribenzotriquinacene. The particular molecular topography of the tribenzotriquinacenes combined with their versatile functionalization renders these compounds promising building blocks for application in molecular and material design.