Condensed Heteroaromatic Ring Systems. VII.¹⁾ Synthesis of Thienopyridines, Thienopyrimidines, and Furopyridines from o-Substituted N-Heteroarylacetylenes

The cross-coupling reaction of 2-chloro-3-iodo- and 4-chloro-3-iodopyridines with phenyl-acetylene in the presence of dichlorobis(triphenylphosphine)palladium occurred at the 3-position. The 3-ethynylpyridines containing an adjacent chloro group were convertible to thienopyridines by treatment with sodium hydrosulfide. Similarly, various thieno[2,3-d]pyrimidines were synthesized from 4-chloro-5-iodopyrimidines. One-step synthesis of furopyridines by the palladium-catalyzed reaction of iodohydroxypyridines with terminal acetylenes is also described.