Ligand‐Controlled Regiodivergent Cyanoboration of Internal Allenes by Copper Catalysis
Hui Hu, Guo‐Cui Ji, Linjuan Jiang, Siwei Bi, Yuan‐Ye Jiang, Yuanhong Liu
Abstract
Abstract The first copper‐catalyzed regiodivergent cyanoboration of internal allenes with B 2 pin 2 (bis(pinacolato)diboron) and NCTS ( N‐ cyano ‐N ‐phenyl‐ p ‐toluenesulfonamide) derivatives is reported. The β,γ‐ and α,β‐cyanoborylated products were synthesized with high regio‐ and stereo‐selectivity. Computational studies revealed that nucleophilic addition of allylcopper or related intermediates on cyanation reagent is the regio‐ and stereo‐determining step, while transmetalation with B 2 pin 2 is the rate‐determining step. The nucleophilic addition step proceeds via inner‐sphere mechanism in the Cu I /P( o ‐tol) 3 and Cu I /Xantphos (P( o ‐tol) 3 =tris( o ‐methylphenyl)phosphine, Xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) catalytic systems and via outer‐sphere mechanism in the Cu II /Xantphos catalytic system, respectively.