New synthetic strategies and disconnections in the synthesis of liquid crystals enabled by photoredox cross-coupling reactions
In this letter we describe the application of metallaphotoredox cross-electrophile couplings to the synthesis of liquid crystals using dual nickel and iridium catalysis. Given the proliferation of aryl and alkyl bromides in liquid crystal research we consider that the silyl-radical mediated cross-coupling of alkyl bromide with an aryl bromide (to afford a direct alkyl–aryl bond) will become an extremely powerful tool in the synthesis of liquid crystalline materials, and we use this to synthesise several well-known materials (PCH32, 5CB, CB7CB and CB15) in a single synthetic step from inexpensive and commercially available building blocks. The metallaphotoredox decarboxylative sp3–sp2 cross-coupling of an aryl bromide with an alkyl carboxylic acid provides a complimentary method to form alkyl–aryl bonds, and we use this to successfully prepare trans PCH5 in a single synthetic step from commercially available building blocks. We also prepare novel methylene-linked materials in a single synthetic step, one of which exhibit the topical TB phase.
