Palladium-Catalyzed Direct Arylation of 4-Chromanones: Selective Synthesis of Racemic Isoflavanones and 3,3-Diaryl-4-chromanones

For the first time, the synthesis of racemic isoflavanones has been achieved in satisfactory to good yields and with high selectivity by Pd-catalyzed direct C-3 arylation of 3-unsubstituted 4-chromanones with aryl bromides with the aid of a Pd2(dba)3/tBu3PHBF4 catalyst system in the presence of KHCO3 as the base in a dioxane/water mixture (4:1). This catalyst system has also been employed in an unprecedented synthesis of 3,3-diaryl-4-chromanones through direct aryl- ation of 4-chromanones in water.