Intramolecular Catalyst Transfer on a Variety of Functional Groups between Benzene Rings in a Suzuki-Miyaura Coupling Reaction

Suzuki-Miyaura coupling reaction of BrC₆ H₄ -X-C₆ H₄ Br 1 (X=CH₂ , CO, N-Bu, O, S, SO, and SO₂ ) with arylboronic acid 2 was investigated in the presence of tBu₃ PPd precatalyst and CsF/[18]crown-6 as a base to establish whether or not the Pd catalyst can undergo catalyst transfer on these functional groups. In the reaction of 1 (X=CH₂ , CO, N-Bu, O, and SO₂ ) with 2, aryl-disubstituted product 3 (Ar-C₆ H₄ -X-C₆ H₄ -Ar) was exclusively obtained, indicating that the Pd catalyst undergoes catalyst transfer on these functional groups. On the other hand, the reaction of 1 e (X=S) and 1 f (X=SO) with 2 afforded only aryl-monosubstituted product 4 (Ar-C₆ H₄ -X-C₆ H₄ -Br) and a mixture of 3 and 4, respectively, indicating that S and SO interfere with intramolecular catalyst transfer. Furthermore, we found that Suzuki-Miyaura polycondensation of 1 (X=CH₂ , CO, N-Bu, O, and SO₂ ) and phenylenediboronic acid 5 in the presence of tBu₃ PPd precatalyst afforded high-molecular-weight polymer even when excess 1 was used. The polymers obtained from 1 (X=CH₂ , N-Bu, and O) and 5 turned out to be cyclic.