Synergistic Rh(ii)/Cu(ii)/PybBox catalysis enables modular access to propargylated benzofuranone and indanone scaffolds.

Herein, we report a synergistic Rh(ii)/Cu(ii)/PyBox catalytic system for the coupling of α-diazo-β-keto esters with propargyl benzoates, enabling modular synthesis of propargylated benzofuranone and indanone derivatives featuring quaternary carbon centers-a motif prevalent in bioactive molecules and functional materials. This transformation proceeds under mild conditions with high efficiency, affording yields of up to 93% and exhibiting broad functional group tolerance toward halogens, electron-donating/withdrawing groups, heteroaryls, and sterically hindered substituents. Notably, the terminal alkyne moiety in products serves as a versatile handle for late-stage derivatization via click chemistry and other transformations. Mechanistic investigations uncover that the PyBox ligand exerts a dual role: promoting the formation of electrophilic Cu-allenylidene species and precisely regulating the generation rate of the nucleophilic Rh(ii)-associated intermediates, thus orchestrating the two catalytic cycles cooperatively. Overall, this work establishes a paradigm for Rh(ii)/Cu(ii) synergistic catalysis and provides a practical modular route to valuable benzofuranone and indanone products with quaternary carbon centers.