Synthesis of the Conjugated Tetraene Acid Side Chain of Mycolactone E by Suzuki-Miyaura Cross-Coupling Reaction of Alkenyl Boronates

The conjugated tetraene acid side chain of mycolactone E has been synthesized by the cross-coupling reaction of a trisubstituted triene bromide with a trisubstituted alkenyl boronate catalyzed by Pd(OAc)(2)-Aphos-Y under mildly basic conditions [K3PO4 center dot 3H(2)O, H2O, tetrahydrofuran (THF), 35 degrees C, 18 h]. The conjugated tetraene product was obtained in 85% yield without geometrical isomer(s) under the catalytic conditions. These results demonstrated that the coupling of alkenyl halides with alkenyl boronates catalyzed by Pd(OAc)(2)-Aphos- Y in combination with Cu-I-catalyzed regio- and stereoselective alkyne borylation offers an efficient synthetic tool for accessing conjugated polyene molecules.