Multicatalytic Stereoselective Synthesis of Highly Substituted Alkenes by Sequential Isomerization/Cross-Coupling Reactions

Starting from readily available alkenyl methyl ethers, the stereoselective preparation of highly substituted alkenes by two complementary multicatalytic sequential isomerization/cross-coupling sequences is described. Both elementary steps of these sequences are challenging processes when considered independently. A cationic iridium catalyst was identified for the stereoselective isomerization of allyl methyl ethers and was found to be compatible with a nickel catalyst for the subsequent cross-coupling of the in situ generated methyl vinyl ethers with various Grignard reagents. The method is compatible with sensitive functional groups and a multitude of olefinic substitution patterns to deliver products with high control of the newly generated C═C bond. A highly enantioselective variant of this [Ir/Ni] sequence has been established using a chiral iridium precatalyst. A complementary [Pd/Ni] catalytic sequence has been optimized for alkenyl methyl ethers with a remote C═C bond. The final alkenes were isolated with a lower level of stereocontrol. Upon proper choice of the Grignard reagent, we demonstrated that C(sp2)—C(sp2) and C(sp2)—C(sp3) bonds can be constructed with both systems delivering products that would be difficult to access by conventional methods