Improvements in cross coupling reactions of hypervalent siloxane derivatives

formula: see text] The scope of the palladium-catalyzed cross coupling reaction of aryl halides with phenyltrimethoxysilane has been expanded to include aryl bromides, heteroaryl bromides, and aryl chlorides. A more general Pd(0)-catalyst/ligand system has been developed to activate bromides: palladium(II) acetate (Pd(OAc)2) is activated with triphenylphosphine (PPh3) or tri-o-tolylphosphine (P(o-tol)3) (1:2 molar ratio of Pd:phosphine). Coupling of aryl chloride derivatives required addition of 2-(dicyclohexylphosphino)biphenyl (Buchwald's ligand) to Pd2dba3 (tris-(dibenzylideneacetone)dipalladium(0)) (1:1.5 molar ratio of Pd:phosphine).