Sequential Suzuki/Suzuki couplings with a dibromoiododiene - A versatile strategy for the stereocontrolled synthesis of polyunsaturated butenolides

In the presence of NaOH and cat. Pd(PPh3)(4), the trihalodiene 4 underwent highly regioselective Suzuki-couplings with unsaturated boronic acids: At 7 0 degrees C, the iodoolefin moiety coupled first (with boronic acid 14) and the E-bromoolefin moiety thereafter (with boronic acid 16). The resulting Z-bromolefin 17 was transformed into the stereopure alpha-alkenyl-gamma-alk ylidenebutenolide 2 in three steps. The strategy developed here should be a pplicable to the synthesis of peridinin (1) which plays a central role in p hotosynthesis by marine algae.