ORGANIC & BIOMOLECULAR CHEMISTRY, vol.2, no.6, pp.852-857, 2004 (SCI-Expanded)
5-Pyrimidylboronic acid 2 and 2-methoxy-5-pyrimidylboronic acid 4 have been synthesised by lithium-halogen exchange reactions on 5-bromopyrimidine and 2-methoxy-5-bromopyrimidine, respectively, followed by reaction with triisopropylborate. Suzuki cross-coupling reactions of 2 and 4 with heteroaryl halides [Na2CO3, Pd(PPh3)(2)Cl-2, 1,4-dioxane, 95 degreesC] yield heteroarylpyrimidines ( heteroaryl = thienyl, quinolyl and pyrimidyl). Two-fold reaction of 2 with 4,6-dichloropyrimidine 12 gave 4,6- bis(5-pyrimidyl) pyrimidine 8 (56% yield). Reaction of 4,6-dichloropyrimidine with 2-methoxy-5-pyridylboronic acid gave 4,6-bis(2-methoxy-5-pyridyl) pyrimidine 14 (84% yield). Conversion of 14 into 4,6- bis(2-chloro-5-pyridyl) pyrimidine 15 (63% yield) followed by two-fold Suzuki reaction with 4-tert-butylbenzeneboronic acid gave the penta-arylene derivative 4,6- bis[2-(4-tert-butyl) phenyl-5-pyridyl] pyrimidine 16 (16% yield). Analogous reaction of 12 with 2- methoxy-3-pyridylboronic acid 17 gave 4,6- bis(2-methoxy-3-pyridyl)pyrimidine 18 (64% yield). The X-ray crystal structures of compound 2 . 0.5H(2)O and compound 18 are reported. The two hydroxyl H atoms in 2 have the usual exo - endo orientation. However, unlike most arylboronic acids, molecule 2 does not form a centrosymmetric hydrogen-bonded dimer. In molecule 18, the pyridine rings form dihedral angles of 39.9degrees and 22.8degrees with the central pyrimidine ring.