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 -[(R 1 NH)(R 2 )methylidene]PdCl 2 (CNR 1 ) [R 1 = 2,4,6-(CH 3 ) 3 C 6 H 2 : R 2 = NC 5 H 10 ( 2 ); NC 4 H 8 ( 3 ); NC 4 H 8 O ( 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-(CH 3 ) 3 C 6 H 2 )NC} 2 PdCl 2 in moderate yields (ca. 61-66%).