Nickel Acetyl Acetonate [Ni(acac)2]

(A) Ni(acac)2-catalyzed couplings of enones, alkynes and main-group organometallic reagents generate acyclic structures in an efficient manner. Ikeda et al. produced conjugated enynes from acetylenic tin reagents. (B) Ni(acac)2 is used in InI-mediated direct allylation of carbonyl compounds with allylic alcohols. The reaction proceeded smoothly with catalytic amounts of Ni(acac)2 and PPh3 to give the corresponding homoallylic alcohols in high yields. (C) Intermolecular coupling of an electron-deficient olefin with a strained olefin using Ni(acac)2 and a modified chiral monodentate oxazoline provides good yields and enantioselectivity. (D) Ni(acac)2-catalyzed cross-coupling between two sp3 carbon centers allows the synthesis of polyfunctional products. (E) Ni(acac)2 promotes the coupling of alkenes with aldehydes in the presence of triethylborane or diethylzinc as reducing agents. Triethylborane-mediated couplings work mainly for aromatic and unsaturated aldehydes, whereas diethylzinc-promoted couplings work best for aliphatic aldehydes and ketones. The reactions proceed well in water or in alcoholic solvents. (F) Ni(acac)2-assisted coupling of 1,7-diynes with silanes produces sixmembered ring products with a Z-configured vinyl silane moiety. (G) Takimoto and Mori developed the Ni(acac)2-assisted coupling of 1,3dienes, CO2, and an organozinc reagent, allowing easy assembly of densely functionalized rings. Terao et al. developed comparable multicomponent coupling of two dienes, a silyl chloride, and a Grignard reagent. The procedure has been extended to asymmetric variants