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. β-Hydrogen elimination from palladium complexes is a fundamental reaction in palladium catalysis. Normally, the eliminated β-hydrogen has to be attached to a sp3-carbon. We envision that the hydrogen elimination from sp2-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 β-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.

Funding source: National Natural Science Foundation of China (91956113, 21772216, 21871284, and 21933009); the Chinese Academy of Sciences (XDB 20020100, XDB20000000 and QYZDY-SSW-SLH026); the Science and Technology Commission of Shanghai Municipality (18401933500, 20XD1423400); the Shanghai Municipal Education Commission (2019-01-07-00-10-E00072)
Related subjects: Production & Supply Chain

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