Direct Heteroarylation: A Modern Synthetic Tool for the Synthesis of Liquid Crystalline Organic Semiconductors M. R. Billa, S. P. Kitney, S.M. Kelly The University of Hull, Department of Chemistry E-mail address: M.R.Billa@2007.hull.ac.uk The conventional method to synthesise liquid crystalline organic electronic materials uses traditional cross coupling reactions such as Suzuki and Stille couplings. However, these conventional methods have drawbacks including the use of organometallic reagents which generate a stoichiometric amount of metal waste which is often toxic, difficult to handle and requires the prior preparation of organometallic precursors and extra synthetic steps. To overcome these difficulties and to avoid using organometallic reagents Pd-catalysed direct heteroarylation is an alternative technique to traditional cross coupling. No preparation of an organometallic derivative is required and most importantly the number of reaction steps is reduced1, 2, 3. Abstract: Optimised reaction Conditions for scheme-1: Reaction time-3 hrs Temperature-100 °C Pd(OAc)2 -2 mol % Pivalic acid-30 mol % K2CO3-2.5 equiv DMF -0.25 Molar Conventional Stille/Suzuki coupling Sheme-2 Direct Heteroarylation Scheme-1 X-ray diffraction: Direct heteroarylation of 2,2’-bithiophene gives a bithiophene-fluorene based oligomer in good yields. The optimised reaction conditions were investigated in terms of the catalytic system and reaction times. The optimised reaction conditions allows the synthesis of 5',5'''-(9,9-dioctylfluorene-2,7-diyl-bis(5- 9,9-dihexyl-7-5'-(4-methoxyphenyl)-[2,2'-bithiophen]-5-yl-fluoren-2-yl -2,2'-bithiophene) in three synthetic reaction steps with an overall yield of 45%, scheme-1. This is in comparison to ten synthetic steps required for more conventional Stille4 or Suzuki-Miyaura aryl-aryl coupling reactions, scheme-2. The reactions all proceed without the addition of a phosphine ligand and the need for use of bifunctional organometallic reagents as reaction intermediates. Nematic phase of compound 1 Advantages: Minimal synthetic steps Higher yields Lower catalyst loadings Does not employ organometallic intermediate Easy purification Eco-friendly Faster Economical Single step synthesis of small molecular weight organic semiconductors The direct heteroarylation condensation reaction is a very promising method to synthesize high molecular weight compounds as well as low molecular weight compounds with high yields in a more environmentally friendly and faster way5. Smectic A phase of compound 2 DSC thermograph of compound 2 Conclusion : Ultimately, by merging the advantages of organic semiconductors with new eco-friendly synthetic procedures, new opportunities for the production of green energy from green materials may emerge. The use of more environmentally friendly materials, which produce no tin/boronic by-products, could also show improved performance and stability. The new synthetic procedure, i.e., direct heteroarylation (scheme-1) allows the synthesis of the same material (scheme-2) but on a larger scale and much more quickly and efficiently. References: 1. Derek J. Schipper and Keith Fagnou, Chem. Mater., 2011, 23 , 1594–1600 Yohei Fujinami, Junpei Kuwabara, Wei Lu, Hideki Hayashi, and Takaki Kanbara, ACS Macro Lett., 2012, 1, 67–70. Julien Roger, Franc Požgan and Henri Doucet Green Chem., 2009, 11, 425-432. J.K. Stille, Angew. Chem. Int. Ed. (1986), 25, p. 508. Philippe Berrouard, Dr. Ahmed Najari, Dr. Agnieszka Pron, David Gendron, Pierre-Olivier Morin, Jean-Rémi Pouliot,  Justine Veilleux, Prof. Dr. Mario Leclerc, 2012, 51, 2068-2071.