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-[(R1NH)­(R2)­methylidene]­PdCl2(CNR1) [R1 = 2,4,6-(CH3)3C6H2: R2 = NC5H10 (2); NC4H8 (3); NC4H8O (4)] were used not only to perform the Csp2–Csp 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)3C6H2)­NC}2PdCl2 in moderate yields (ca. 61–66%).