An alternative method to copper-catalyzed conjugate addition followed by enolate silylation for the synthesis of β-di-substituted silyl enol ether products (R1(R2)HCCH=C(OSiR43)R3) is presented. This method uses haloarenes instead of nucleophilic aryl reagents. Nickel ligated to either neocuproine or bipyridine couples an α,β-unsaturated ketone or aldehyde (R2HC=CHC(O)R3) with an organic halide (R1-X) in the presence of a trialkylchlorosilane reagent (Cl-SiR43). Reactions are assembled on the bench-top and tolerate a variety of functional groups (aldehyde, ketone, nitrile, sulfone, pentafluorosulfur, and N-aryltrifluoroacetamide), electron-rich iodoarenes, and electron-poor haloarenes. Mechanistic studies have confirmed the first example of a catalytic reductive conjugate addition of organic halides that proceeds via an allylnickel intermediate. Selectivity is attributed to: 1) rapid, selective reaction of LNi0 with chlorotriethylsilane and enone in the presence of other organic electrophiles, and 2) minimization of enone dimerization by ligand steric effects.
The direct, regioselective, and stereoselective arylation of activated alkynes with aryl iodides using a nickel catalyst and manganese reductant is described. The reaction conditions are mild (40 °C in MeOH, no acid or base) and an intermediate organomanganese reagent is unlikely. Functional groups tolerated include halides and pseudohalides, free and protected anilines, and a benzyl alcohol. Other activated alkynes including an amide and a ketone also reacted to form arylated products in good yields.
Nickel-Catalyzed Reductive Conjugate Addition to Enones via Allylnickel Intermediates. -In comparison to related copper-catalyzed procedures the presented protocol utilizes readily accessible haloarenes instead of nucleophilic aryl reagents. A wide variety of functional groups is tolerated. From a mechanistic point of view these are the first examples for a catalytic reductive conjugate addition of organic halides via allylnickel intermediates. -(SHRESTHA, R.; DORN, S. C. M.; WEIX*, D. J.; J. Am. Chem. Soc. 135 (2013) 2, 751-762, http://dx.doi.org/10.1021/ja309176h ; Dep. Chem., Univ. Rochester, Rochester, NY 14627, USA; Eng.) -Nuesgen 33-036
In Gegenwart von Perfluorbutylsulfonat (C4F9SO3H) reagieren die Pyrrole (I) mit den entsprechenden (II) zu Gemischen aus den disubstituierten Pyrrolen (III) und (IV).
Nickel-Catalyzed Reductive Arylation of Activated Alkynes with Aryl Iodides. -The title reaction proceeds with high regio-and stereoselectivity to provide (E)--aryl alkenoates as major products. Aryl iodides (IIh) and (IIi) also give significant amounts of -addition products. -(DORN, S. C. M.; OLSEN, A. K.; KELEMEN, R. E.; SHRESTHA, R.; WEIX*, D. J.; Tetrahedron Lett. 56 (2015) 23, 3365-3367, http://dx.
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