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 <i>cis</i>-[(R¹NH)­(R²)­methylidene]­PdCl₂(CNR¹) [R¹ = 2,4,6-(CH₃)₃C₆H₂: R² = NC₅H₁₀ (<b>2</b>); NC₄H₈ (<b>3</b>); NC₄H₈O (<b>4</b>)] were used not only to perform the C_sp²–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 (<b>2</b>–<b>4</b>) were conveniently synthesized by the nucleophilic addition of secondary amines, namely, piperidine, pyrrolidine, and morpholine on the <i>cis</i>-{(2,4,6-(CH₃)₃C₆H₂)­NC}₂PdCl₂ in moderate yields (ca. 61–66%)