Organozinc reagents nickel catalysts

Inspired by the well-established nickel-catalyzed co-oligomerization of 1,3-dienes with CO2, which proceeds via bis-TT-allyl intermediate, Mori has developed a powerful intramolecular version of this process (Scheme 103). After insertion of C02 into the bis-vr-allyl complex, a transmetallation with an organozinc reagent takes place to generate the Ni(0) catalyst. Highly functionalized carbo- and heterocyclic compounds with complete stereocontrol can372 be synthesized by this method. 

The most often-reported metallic systems used in the formation of carboxylic acids are most certainly those systems that involve a zero-valent nickel species as the active intermediate. Ochiai et al. reported on a bimetallic catalytic system which allowed the synthesis of various saturated carboxylic acid in good yields, under very mild conditions [53] (0.1 MPa C02, 4—8 h reaction time, temperatures ranging from room temperature to 323 K). The catalytic system was based on the use of organozinc reagents as carbon nucleophiles, which could be selectively carboxy-lated in the presence of Ni(acac)2 as the main catalyst. 

The copper-catalyzed conjugate addition reaction of organozinc reagents has reached a prominent level of success by the development of sophisticated chiral phosphorus ligands. Nickel catalysts have also been surveyed by several groups. 

From these results, it can be concluded that the mild conditions and nickel catalyst have resulted in a wider tolerance of functional groups and a greater scope of the reactions. Significantly, this strategy affords a more economically and environmentally useful and valuable synthetic procedure for the preparation of ketones utilizing organozinc reagents, which are readily available. 

Lipshutz showed that nickel on charcoal ( Ni/C ) was found to be an efficient heterogeneous catalyst for mediating carbon-carbon bond constructions involving chloroarenes 28 and functionalized organozinc reagents to give 29 Importantly retention of nickel on the solid support offers control over such critical parameters as waste disposal and toxicity. 

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