One-Pot Tandem Hiyama Alkynylation/Cyclizations by Palladium(II) Acyclic Diaminocarbene (ADC) Complexes Yielding Biologically Relevant Benzofuran Scaffolds

A series of palladium acyclic diaminocarbene (ADC) complexes of the type cis-[((RNH)-N-1)(R-2)methylidene]-PdCl2(CNR1) [R-1 = 2,4,6-(CH3)(3)C6H2: R-2 = NC5H10 (2); NC4H8 (3); NC4H8O (4)] were used not only to perform the C-sp(2)-C-sp Hiyama coupling between aryl iodide and triethoxysilylalkynes but also to subsequently carry out the one-pot tandem Hiyama alkynylation/cyclization reaction between 2-iodophenol and triethoxysilylalkynes, giving a convenient time-efficient access to the biologically relevant benzofuran compounds. The palladium ADC complexes (2-4) were conveniently synthesized by the nucleophilic addition of secondary amines, namely, piperidine, pyrrolidine, and morpholine on the cis-{(2,4,6-(CH3)(3)C6H2)NC}(2)PdCl2 in moderate yields (ca. 61-66%)