THE CYANATION OF VINYL HALIDES WITH ALKALI CYANIDES CATALYZED BY NICKEL(O)-PHOSPHINE COMPLEXES GENERATED IN-SITU - SYNTHETIC AND STEREOCHEMICAL ASPECTS

The cyanation of beta-bromostyrenes catalyzed by Ni(PPh(3))(n), which was generated in situ from NiBr2(PPh(3))(2)-Zn-PPh(3) (Ni:Zn:P=1:3:2 molar ratio), was at first examined with various MCN (M=K, Na)-dipolar aprotic solvent systems by several procedures. The presence of excess cyanide ion inhibited the reaction. However, when the KCN-DMF system with some intermediate cyanide solubility was used, the nitriles were obtained in high yields and high stereoselectivity at 50 degrees C by almost all of the procedures attempted. On the contrary, the KCN-HMPA and KCN-MeCN systems with low cyanide solubilities accelerated the coupling of the halides to inhibit the cyanation, and in general the NaCN-DMF and NaCN-HMPA systems with high cyanide solubilities needed to reduce Ni(II) before adding MCN in order to make the catalytic reaction start. Vinyl halides such as 1- and 2-halo (Cl, Br)-1-alkenes, 2-bromo-2-butenes, 3-bromo-3-hexenes, and 1-chlorocyclohexene were also cyanated using suitable procedures and MCN-solvent systems to give the corresponding nitriles in high yields and fair-to-good stereoselectivities. However, with (2)-2-ethoxy-1-bromoethene the (E)-nitrile, though its selectivity markedly varied with the reaction temperature, was obtained as the main product. The cyanation of ethyl (Z)-beta-bromoacrylate and ethyl alpha-bromoacrylate was unsuccessful due to polymerization.