3, 5-Dimethyl-4-iodoisoxazole (1a) reacted with phenylacetylene with catalysis by palladium (II) chloride-triphenylphosphine complex to give 3, 5-dimethyl-4-phenylethynyl-isoxazole (2a). When 1a was treated with styrene under similar conditions, 3, 5-dimethyl-4-trans-styrylisoxazole (3a) was obtained. In contrast, the palladium-catalyzed crosscoupling reaction of 3-phenyl-5-bromoisoxazole (4) with styrene afforded 3, 3'-diphenyl-5, 5'-biisoxazole (6) as the main product, instead of the desired styryl compound (5a). However, 3-phenyl-5-phenylethynylisoxazole (7a) was obtained, as in the case of 1a, by the reaction of 4 with phenylacetylene. Some additional examples of these coupling reactions are also described.
