Palladium organozinc reagents

Organozinc reagents are also used extensively in conjunction with palladium in a number of carbon-carbon bond-forming processes that are discussed in Section 8.2. 

Scheme 6.43 Palladium-catalyzed a-arylation of esters and amides with organozinc reagents.

Crucially, this allows organozinc reagents to be prepared from less reactive aryl bromides and secondary or tertiary alkyl bromides. Alternatively, organozinc iodides can be prepared by means of a palladium(0)-catalyzed reaction between alkyl iodides and Et2Zn (Scheme 2.25) [53-56]. 

Enantioselective alkylative ring opening of these oxabicyclic alkenes has also been studied. Lautens and coworkers discovered that palladium complexes efficiently catalyze the addition of organozinc reagents to these activated alkenes with concomitant ring opening. In the presence of (Tol-BINAP)PdCl2, diethylzinc adds to oxabenzonor-... 

A prototypical study for this section has been obtained as early as in 1983 for carbonylative cross-coupling of the mixture of aryl iodide and alkyl iodide in the presence of Zn metal and palladium catalyst. This system apparently works due to differences of reactivity of aryl versus alkyl iodide toward metallation by Zn. Further studies were rather scarce to involve only preformed functionalized alkylzincs. Carbonylative cross-coupling of functionalized organozinc reagents with allylic esters and GO (1 atm) can be carried out in THF in the presence of HMPA, which suppresses side-reactions (Scheme 4). ... 

Organozinc reagents, including the Reformatsky reagents, are extensively used in transition metal catalysed coupling reactions with aryl halides or triflates, vinyl halides, and allylic halides or acetates, as reviewed by Erdik156. Nickel and palladium complexes are... 

In several of the previously described methods the anion of the three-carbon fragments was added to an a-amino aldehyde to construct a C—C bond between the C3 and C4 atoms of the 1-hydroxyethylene isostere. However, Sakurai et al.[27l used an add chloride instead of an a-amino aldehyde. They synthesized 6-phthalimido-y-oxo esters by a palladium-catalyzed reaction between acid chlorides and organozinc reagents derived from p-iodo esters. Then, the oxo esters were converted into the y-lactone precursors. 

Organozinc reagents and tetrakis(triphenylphosphine(palladium catalyst have been employed to convert (5)- and (R)-propargylic carbonates of type (211) into chiral allenes such as (212a,b) with ee of 82-85%.180... 

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