Transmetalation of Functionalized Organozinc Reagents

Organozinc compounds have been known for more than 150 years, but their application in organic synthesis was formerly rather limited [39], due to their 

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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. 

In contrast to the polar nature of C-Li and C-MgX bonds, the C-Zn bond is highly covalent and hence less reactive, allowing the preparation of functionalized derivatives. Utilization of organozinc reagents in organic synthesis has mainly centered around the preparation and utilization of functional organozinc compounds in organic syntheses (Reformatsky reaction), cyclopropanation (Simmons-Smith reaction), and transmetalations with transition metals. 

The advantages of using organozinc reagents for cross-coupling reactions are efficient transmetalation to palladium and ready availability, even directly from functionalized halides... 

When the Pd-catalyzed exchange protocol was applied to the 5-alkenyl iodides of type 51, the cyclized organozinc reagents 52 were directly obtained and functionalized by allylation with ethyl 2-bromomethylacrylate after transmetallation with CuCN 2LiCl. The five-membered ring products 53 were obtained with high trans diastereoselectivity, irrespective of the nature of the allylic substituent (R = Ph or OBz) at the allylic position (equation 21)34,39. By contrast, the zinc-induced carbocychzations were found to be moderately cis stereoselective when an acyloxy group was present at the allylic position (see Section II.B.2)29. 

Subsequent developments indicated that transmetallation to copper was also possible in both catalytic and stoichiometric senses, with the use of the THF soluble copper salt CuCN.2LiCl being especially convenient.7 The formation of these functionalized copper reagents has allowed a substantial increase in the range of products which may be prepared from organozinc halides.8... 

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