Cascade Copper-Catalyzed 1,2,3-Trifunctionalization of Terminal Allenes.

A cascade cyanation/diborylation of terminal allenes proceeds efficiently with copper catalysis using bis(pinacolato)diboron (B2Pin2) and N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) as reagents. Mechanistic studies suggest that the process proceeds through cyanoborylation of the substituted π-system of the allene followed by hydroboration of the remaining π-component. A wide array of product derivatives may be accessed through site-selective cross-couplings and N-bromosuccinimide-promoted heteroarylations as well as standard oxidative and reductive conversions of the initially obtained adducts.