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Synthesis of Tetrasubstituted Allenes via Palladium-Catalyzed Cross-Coupling of Vinyl Bromides with Diazo Compounds

A highly efficient palladium-catalyzed cross-coupling of 2,2-diarylvinyl bromides with diazo compounds was developed, providing a convenient approach for the synthesis of tetrasubsti-tuted allenes. Both aryl diazo carbonyl compounds and N-tosylhydrazones are competent carbene precursors in this reaction. An unprecedented hydrogen elimination of the π-allyl palladium intermediate is proposed to be the key step.