NiCl2 and NiCl2 = 6H2O: A very useful mild lewis acid in organic synthesis

Abstract

(A) Suzuki cross-coupling with ArBr and ArI can be carried out with PhB(OH)2 in good yields using NiCl2·6H2O as a catalyst precursor. (B) NiCl2-(1,3-butadiene) catalyzes the cross-coupling reaction of alkyl chlorides, bromides, and tosylates with Grignard reagents under mild conditions. (C) A general and convenient preparation of unsymmetrical N,N′-carbodiimides was achieved by the nickel(II)-catalyzed reaction of isocyanides with primary amines using molecular oxygen as an oxidant. (D) Aryl halides are readily homocoupled using a catalytic amount of NiCl2/CrCl2 and bipyridyl-type ligand 1 in the presence of manganese at room temperature in good yield. (E) Azides are efficiently reduced to the corresponding amines with Sm/NiCl2·6H2O in excellent yields under mild conditions. (F) Nitriles are rapidly reduce to primary amines with nickel boride at room temperature. (F) A Biginelli reaction was efficiently used for the synthesis of 3,4-dihydropyrimidinones from aldehydes, β-keto esters and urea in ethanol, using NiCl2·6H2O. (G) An intramolecular Nozaki-Kishi cyclization was efficiently employed in the cyclization of Z-vinyl bromides to the corresponding cyclopentenols in good yields. (H) In the presence of moist alumina, aliphatic and aromatic alkenes were hydrogenated quantitatively to alkanes under mild conditions with NaBH4/NiCl2.