Palladium-catalyzed allene synthesis enabled by β-hydrogen elimination from sp2-carbon
Ge Zhang, Yi‐Kang Song, Fang Zhang, Ze‐Jian Xue, Mengyao Li, Gui-Shan Zhang, Bin‐Bin Zhu, Jing Wei, Chunsen Li, Chen‐Guo Feng, Guo‐Qiang Lin
Abstract
Abstract 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 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 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.