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. Several alkynyl-substituted fluorinated benzene derivatives have been prepared by cross-coupling reactions of 1,4-dibromo-2-fluorobenzene. The reactions proceed with very good site-selectivity in favor of the 4-position. The regioselectivity is explained by the results of DFT calculations. Thefluorescence properties of the products have been studied. In addition, the mesomorphic properties have been investigated.