The direct C4-arylation of 3,5-dimethylisoxazole with aryl bromides catalyzed by imidazolidin-2-ylidene based palladium-PEPPSI complexes

In this study, the synthesis and characterization of four new imidazolinium salts as carbene precursors and their corresponding four new PEPPSI-type (PEPPSI = Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) palladium complexes were reported. The structures of these new compounds were characterized by spectroscopic and analytical techniques. The catalytic activities of all palladium complexes were evaluated in the direct C4-arylation of 3,5-dimethylisoxazole with para-substituted aryl bromides, ortho-substituted aryl bromides and heteroaryl bromides. A range of functional groups such as methoxy, acetyl, formyl, fluoro, trifluoromethyl, nitrile or tert-butyl on the aryl bromide were succesfully tolerated, and good yields were generally obtained in presence of 1 mol% catalyst loading at 120 degrees C.