Microwave-assisted palladium-catalyzed C-C coupling versus nucleophilic aromatic substitution of hydrogen (SNH) in 5-bromopyrimidine by action of bithiophene and its analogues

Article abstract of DOI:10.1016/j.tet.2013.04.062

5-Bromopyrimidine reacts with 2,2′-bithiophene, [2,2′:5′, 2″]terthiophene and 2-phenylthiophene in the presence of a palladium catalyst to give 5-(het)aryl substituted pyrimidines due to the palladium-catalyzed aryl-aryl C-C coupling. However 5-bromo-4-(het)aryl- pyrimidines have been prepared from the same starting materials through the S_N^H-reaction catalyzed by a Lewis acid. Conditions for both types of reactions were optimized. All components of the reaction mixtures, including by-products, have been elucidated by gas-liquid chromatography/mass- spectrometry. Evidence for the structure of 4- and 5-bithiophenyl-substituted pyrimidines has first been obtained by means of X-ray crystallography analysis. Molecular orbital calculations (TDDFT), as well as the redox and optical measurements for all new compounds have also been performed.