Site‐Selective Sonogashira Reactions of 1,4‐Dibromo‐2‐fluorobenzene – Synthesis and Properties of Fluorinated Alkynylbenzenes

A variety of alkynyl‐substituted fluorinated benzene derivatives have been prepared by Sonogashira cross‐coupling reactions of 1,4‐dibromo‐2‐fluorobenzene. The reactions proceed with very good site‐selectivity in favor of the 4‐position because of electronic and steric reasons. The regioselectivity is explained by the results of DFT calculations. The absorption and emission (fluorescence) properties of the products, mono‐ and dialkynylated fluorobenzenes, have been studied. In addition, the mesomorphic properties of the products have been investigated by polarization microscopy and differential scanning calorimetry. 1,4‐Dialkynyl‐2‐fluorobenzenes show nematic liquid‐crystalline properties over a long phase range.