Pd(0)-mediated umpolung reaction of the alkyne to access trans-difunctionalization is a potential synthetic methodology, but its insightful activation mechanism of Pd(0)-alkyne interaction has yet to be established. Here, a Pd(0)-π-Lewis base activation mode is proposed and investigated by combining theoretical and experimental studies. In this activation mode, the Pd(0) coordinates to the alkyne group and enhances its nucleophilicity through π-back-donation, facilitating the nucleophilic attack on the aldehyde to generate the trans-Pd(II)-vinyl complex. Ligand-effect studies reveal the more elec-tron-donating one would accelerate the reaction, and the cyclization for the challenging flexible C- or O-tethered substrates has been realized. The origin of regioselectivities is also explicated by the newly proposed metal π-Lewis base activation mode.

This article is Open Access

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