Palladium catalyzed cross-coupling reactions of allyl- and vinylsilanes

Palladium-catalyzed cross-coupling of ??-substituted allylic silanolates with aryl bromides was investigated. It was discovered that ??-selectivity is heavily influenced by the substituents at silicon. It is proposed that undergoing an activated pathway significantly lowers the selectivity of the reaction. A major side-product of this reaction was discovered and conditions were developed to suppress the undesired reaction. It is proposed that the side reaction shares at least two intermediates with the desired cross-coupling reaction. The use of arsenic ligands and elevated temperatures mildly suppressed the side-reaction and further studies are needed to completely prevent the unwanted pathway from occurring. The development and application of a 1,2-differentiated bissilylethene moiety has been studied. Moderate yields are obtained in the fluoride-free coupling with aryl iodides under mild conditions. When the cross-coupling reaction is conducted with aryl bromides poor yields of the desired product are obtained. The reactive silanolate species was discovered to dimerize to a non-competent disiloxane species at elevated temperatures. Hemilabile phosphine ligands and basic additives can be employed to facilitate the cross-coupling with aryl bromides; however, further studies are needed to prevent dimerization of the silanolate from occurring