Understanding Site Selectivity in the Palladium-Catalyzed Cross-Coupling of Allenylsilanolates

Allenylsilanolates can undergo cross-coupling at the α- or γ-terminus, and site selectivity appears to be determined by the intrinsic transmetalation mechanism. Fine-tuning of concentration, nucleophilicity, and steric bulk of the silanolate moiety allows for the selective formation of one isomer over the other. Whereas the α-isomer can be obtained in synthetically useful yield, the γ-isomer is favored only when employing reaction conditions that are inevitably associated with diminished reactivity.