78. Ligand-Controlled Regiodivergent Cyanoboration of Internal Allenes by Copper Catalysis

Hu, H.;# Ji, G.-C.;# Jiang, L.;# Bi, S.; Jiang, Y.-Y.;* Liu, Y.*  Angew. Chem. Int. Ed. 2022, 61, e202210338. Download Link

Abstract: The first copper-catalyzed regiodivergent cyanoboration of internal allenes with B2pin2 (bis(pinacolato)diboron) and NCTS (N-cyano-N-phenylp-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 regioand stereo-determining step, while transmetalation with B2pin2 is the rate-determining step. The nucleophilic addition step proceeds via inner-sphere mechanism in the CuI/P(o-tol)3 and CuI/Xantphos (P(o-tol)3=tris(omethylphenyl)phosphine, Xantphos=4,5- bis(diphenylphosphino)-9,9-dimethylxanthene) catalytic systems and via outer-sphere mechanism in the CuII/Xantphos catalytic system, respectively.