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%).