The Diyne Reaction of 3, 3′‐Bis(phenylethynyl)‐2, 2′‐bithiophene Derivatives via Rhodium Complexes: A novel approach to condensed benzo[2, 1‐b :3, 4‐b′]dithiophenes

The syntheses of benzo‐fused benzo[2, 1‐ b :3, 4‐ b ′]dithiophenes 1 and benzo[2, 1‐ b :3, 4‐ b ′:5, 6‐ c ″]trithiophenes 2 are described. The treatment of easily available 3, 3′‐bis(phenylethynyl)‐2, 2′‐bithiophene derivatives 5a and 6 ( via Pd II ‐catalyzed alkynylation of the corresponding 3, 3′‐dibromo‐2, 2′‐bithiophenes; see Scheme 1 ) with chlorotris‐(triphenylphosphine)rhodium(I) yields the corresponding cyclic rhodium complexes 7 ( Scheme 2 ) which smoothly react with acetylenes and sulfur to give 1 and 2 in good yields ( Schemes 3–5 ).