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 (B(2)Pin(2)) and N-cyano-N-phenyl-pmethylbenzenesulfonamide (NCTS) as reagents. Mechanistic studies suggest that the process proceeds through cyanoborylation of the substituted mu-system of the allene followed by hydroboration of the remaining mu-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.