Synthesis of Polyfunctionalized Biphenyls as Intermediates for a New Class of Liquid Crystals

A series of hexa- and octasubstituted biphenyls containing halogen, amino, nitro, and propylthio substituents were prepared by metal-mediated convergent synthesis from halobenzene precursors. The Pd-assisted C-C coupling methods were ineffective in the formation of the Ar-Ar bond except for the synthesis of 1b. All tetra-ortho-substituted biphenyls were prepared via Ullmann coupling reactions. The halogens were introduced after formation of the biphenyl by utilizing the directing properties of the amino group(s). In the case of 3b, a polyhalogenated benzene substrate was used for biphenyl formation via Ullmann coupling.