Synthesis and reactions of new N-heteroaryl boronic acids

Abstract

New functionalized pyridazinylboronic acids/esters are reported. A comprehensive study of the reactivity of the C-B bond in palladium-catalyzed cross-couplings with aryl/heteroaryl halides is presented. Aryl/heteroaryl-pyridazines have thereby been obtained in synthetically viable yields (typically 40-75%). A series of pyridazin-3 (2H) - one derivatives have been obtained from the corresponding 3-methoxypyridazines in straightforward procedures. Further functionalization of the pyridazin-3 (2H)-one derivatives through C-C and C-N cross-coupling reactions yielded a number of multiheteroaryl arrays. The synthesis of trifluoromethyl-substituted pyridylboronic acids and pyrazolylboronic esters is described. An extensive study of their palladium-catalyzed cross-couplings with aryl/heteroaryl halides is presented. СF(_3)-substituted aryl/heteroaryl-pyridines have thereby been obtained (51-98% yields). Analogous cross-couplings have yielded heteroaryl-3-(trifluoromethyl)pyrazoles (60-85% yields). Regioselective halogenation of the 4-position of selected trifluoromethylated pyrazole derivatives was successful. Subsequent Suzuki-Miyaura cross-couplings yielded tetra-substituted pyrazolyl derivatives. X-Ray crystal structures are reported for several aryl/heteroaryl-pyridazines and derived pyridazin-3 (2H)-one derivatives, and selected pyridylboronic acids, pyrazolylboronic esters and derived trifluoromethyl-substituted heterobiaryl systems.