“Cesium Effect”-Mediated/Controlled Divergent Synthesis via Synergistic Pd/Cu-Catalyzed Cascade Reactions

Abstract

Herein, we describe a method in the one-pot synthesis of cyclic 1,3-enynes and allenynes from alkynyl-allenyl cross-coupling and cascade reactions of vinylidenecyclopropane-diesters (VDCP-diesters) with a large number of unactivated terminal alkynes for the formation of a C(sp²)–C(sp) bond under palladium/copper dual catalysis and assisted by base Cs₂CO₃ and NEt₃ with distinctly different Brønsted basicity and Lewis basicity. This developed divergent transformation proceeds through a key rapid transmetalation and the subsequent intramolecular cyclization process regulated by cesium effect. Our investigations found that these reactions can occur under mild conditions and have a broad substrate scope with a wide range of functional groups via a zwitterionic palladium species, affording the corresponding desired products in moderate to good yields. Further synthetic transformations show the application value of this protocol. Plausible reaction mechanisms have also been proposed on the basis of control, deuterium labeling experiments, and density functional theory calculations.