Palladium-catalyzed Carbonylation of Organic Halides with Terminal Acetylenes in the Presence of Amines --Novel Acetylenic Ketone Synth esis--

Abstract

Organic halides were found to be catalytically carbonylated with terminal acetylenes by palladium complexes in the presence of bases under the conditions of P_(co) =20 atm and 120°C to give acetylenic ketones (eg. Equation 1). The basicity of phosphines as ligands for the palladium complex catalysts and, in case of diphosphines, the methylene chain length or the framework between the two phosphino groups profoundly affected the reactivity of the catalysts (Table 1). Arsines were found to accelerate the migratory insertion of carbon monoxide as compared to phosphines (Fig.1). Thus, in terms of the catalytic activity and the selectivity for 1, 3-dipheny1-2-propyn-1-one (DPP) in iodobenzene-phenylacetylene reactions, dppb, dbpb, dcpb, dppf, and dpaf were the ligands of choice. Although low pressure of carbon monoxide (eg.5 atm) was unfavorable for a high DPP selectivity in the PdCl₂(PPh₃)₂- catalyzed reaction, the use of PdCl₂(dppf) allowed the reaction to proceed with high selectivity for DPP even under atmospheric pressure of carbon monoxide (Table 2). Use of strong bases such as triethylamine and tripropylamine was essential for high yield synthesis of DPP (Table 3). This new reaction could be successfully applied to a variety of aromatic, heteroaromatic, and vinylic halides combined with terminal acetylenes except unsubstituted acetylene, which gave intractable tarry material (Table 4).