Deoxygenative C–C Bond-Forming Processes via a Net Four-Electron Reductive Coupling

The nickel-catalyzed
coupling of enones or enals with alkynes in
the presence of silane and titanium alkoxide reductants provides direct
access to skipped diene products. The process involves a net four-electron
reductive coupling and proceeds with deoxygenation of the starting
enone or enal. A new class of well-defined nickel(0) precatalysts
bearing an unhindered N-heterocyclic carbene ligand, which was developed
in optimization of the process, is essential for the efficiency of
the transformation. The strategy allows the high reactivity of α,β-unsaturated
carbonyl substrates to be utilized in couplings with simultaneous
extrusion of the oxygen atom, thus enabling a traceless strategy for
alkene installation.