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

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.