2,3-Disubstituted and 2,3,5-trisubstituted benzofurans by regioselective Pd-catalyzed cross-coupling reactions; a short synthesis of eupomatenoid-15

2,3-Dibromobenzofuran (1) and 2,3,5-tribromobenzofuran (2) undergo regiosel ective Sonogashira- and Negishi-type cross-coupling reactions at the 2-posi tion. Subsequent substitution reactions at C-3 are possible for the cross-c oupling products obtained from compound 1. A regioselective functionalizati on of the 3,5-dibromobenzofurans derived from substrate 2 was achieved by a n halogen-metal exchange which occurred selectively at the 3-position. in a conclusive reaction step cross-coupling reactions at C-5 were used to buil d up 2.3.5-trisubstituted benzofurans. As an example, the synthesis of eupo matenoid-15 (8) is described.