Suzuki-miyaura cross-coupling of 3,4-disubstituted 5-bromoisoxazoles: An efficient access to trisubstituted isoxazoles

Abstract The Suzuki-Miyaura cross-coupling of 3,4-disubstituted 5-bromoisoxazoles 1 at the C5 position has successfully proceeded in the presence of Pd2(dba)3 and P(t-Bu)3·HBF4 catalysts to give the corresponding trisubstituted isoxazoles 3 in good to high yields while suppressing the formation of ketone 4 as a byproduct. The use of bulky phosphine ligand P(t-Bu)3·HBF4 is essential for the current transformation, and the formation of ketone 4, which was a major product in the previous report, was able to be suppressed under the current conditions.