Impregnated palladium on magnetite as catalyst for direct arylation of heterocycles

Palladium impregnated on magnetite is an efficient, cheap and easy to prepare catalyst for the direct arylation of heterocycles. Good yields are afforded under relatively mild conditions and a broad substrate scope is evident. The catalyst is regioselective in many cases, affording arylated products, at the C2- or C3-position (depending of the heterocycle used). The methodology can be extended to prepare chromenes through an intramolecular direct arylation reaction. Some evidence is provided for two catalyst deactivation pathways, which prevents efficient recycling.

Synthesis of 5-Carbapterocarpens by α-Arylation of Tetralones Followed by One-Pot Demethylation/Cyclization with BBr3

5-Carbapterocarpens, one of them displaying estrogenic activity, were prepared from α-aryltetralones in high yields through a one-pot, BBr3-promoted O-demethylation and cyclization sequence. The key α-aryltetralone intermediates were obtained by direct α-arylation of tetralones with o-alkoxybromoarenes in the presence of Pd2(dba)3 (2.5 mol-%) and tBu3PHBF4 (10 mol-%) as catalysts, together with 2.5 equiv. of KOH in dioxane/H2O (4:1), under microwave irradiation conditions (80 W, 100 °C, 40 min), leading to α-monoaryltetralones in good yields.