Palladium-Catalyzed Acylcyanation of Terminal Arylacetylenes. Synthesis of 1,3-Diaryl-3-cyano-2-propen-1-ones and Tetrasubstituted Furans

Article abstract of DOI:10.1246/bcsj.69.1629

(Z)-1,3-Diaryl-3-cyano-2-propen-1-ones ((Z)-1) are prepared from arenecarbonyl cyanide and terminal arylacetylene in the presence of Pd(OAc)₂-PPh₃ (1 mol amt. to Pd)-0.5dppb (1,4-bis(diphenylphosphino)butane) (0.5 mol amt. to Pd). The reaction proceeded via the formation of acetylenic ketone 3, followed by the palladium-catalyzed addition of HCN, and isomerization of the resulting (E)-1 to (Z)-1. Oxidative addition of arenecarbonyl cyanide to zero-valent palladium metal has been observed by admixture of 4-MeOC₆H₄COCN to Pd₂(dba)₃ · CHCl₃-PPh₃-0.5dppb oxide (dppb oxide = Ph₂P(O)(CH₂)₄P(O)Ph₂). The resulting Pd(4-MeOC₆H₄CO)(CN)(PPh₃)(ligand) afforded (Z)-1c by reaction with phenylacetylene. Thus, the role of two kinds of phosphine, PPh₃ and dppb, suggests that the former acts as a ligand and the latter works as a reductant of Pd(II). The product (Z)-1 can be photoisomerized to (E)-1 under room light in CDCl₃. The product (Z)-1 was obtained by a four-component coupling reaction of 4-iodotoluene, phenylacetylene, KCN, and carbon monoxide. A new synthesis of tetrasubstituted furans is also mentioned.