Palladium-catalyzed allene synthesis enabled by β-hydrogen elimination from sp2-carbon

The rational design based on a deep understanding of the present reaction mechanism is an important, viable approach to discover new organic transformations. beta -Hydrogen elimination from palladium complexes is a fundamental reaction in palladium catalysis. Normally, the eliminated beta -hydrogen has to be attached to a sp(3)-carbon. We envision that the hydrogen elimination from sp(2)-carbon is possible by using thoroughly designed reaction systems, which may offer a new strategy for the preparation of allenes. Here, we describe a palladium-catalyzed cross-coupling of 2,2-diarylvinyl bromides and diazo compounds, where a beta -vinylic hydrogen elimination from allylic palladium intermediate is proposed to be the key step. Both aryl diazo carbonyl compounds and N-tosylhydrazones are competent carbene precursors in this reaction. The reaction mechanism is explored by control experiments, KIE studies and DFT calculations.beta -Hydrogen elimination is a fundamental reaction in palladium catalysis, however, the eliminated beta -hydrogen is usually attached to a sp(3)-carbon. Here, the authors report a palladium-catalyzed cross-coupling reaction involving a beta -vinylic hydrogen elimination from an allylic palladium intermediate.

Automated summary

The authors present a palladium-catalyzed cross-coupling reaction involving a beta-vinylic hydrogen elimination from an allylic palladium intermediate.