Negishi reagent

There are several methods for generating low-valent zirconocene species in situ. Although the conventional method has been the reduction of Cp2ZrCl2 with Na/Hg or Mg/Hg, more convenient methods have since been developed for the preparation of symmetrical zirconacyclopentadienes such as Cp2ZrBu2 2 [the so-called Negishi reagent (Eq. 2.2)] [12]. 

Nugent has isolated and structurally characterised the zirconocyclopentanes derived from 1,6-heptadiene and either Cp2ZrCl2/2BuLi or Cp ZrCl3/Na(Hg). The former 25 is monomeric while the latter 25a involved a Zr2(p-Cl)2 structure. However, of particular note is that while the Negishi reagent provides primarily (97 3)... 

A similar, albeit more complex, reactivity manifold is reported for the formation of the Negishi reagent starting from bis( -butyl)zirconocene, which inter alia decomposes to give the putative zirconocene butene complex. Among the compounds identified in this mixture is a labile 2-methylzirconacyclobutane complex <19970M1452>. 

Vinyloxiranes react with the Negishi-reagent [Cp2ZrBu2] by means of deoxygenation to yield conjugated dienes. This reaction is likely to... 

Negishi reaction, 269 Negishi reagent, 129 Nickel complexes, 43 15 Nitrile reactions with... 

Zirconaaziridine synthesis via the Negishi reagent [22,24,28,31,32] is a particularly efficient approach for zirconaaziridines that cannot be prepared by the C-H activation pathway. For example, addition of a hydrazone to zirconocene yields an AT-amino-substituted zirconaaziridine (see Sect. 4.1). The ligand-free 2i, produced in low yield by the C-H activation pathway, can be prepared from zirconocene and an imine/enamine mix as shown in Eq. 6 [24]. 

Scheme 4 Diastereomer ratio of zirconaaziridine and amino alcohol product of aldehyde insertion under thermodynamic and kinetic conditions for zirconaaziridine formation from the Negishi reagent...

The double arylation reaction (Scheme 10.98, path B) also proceeded in this case to form the desired product 294, albeit in low yield. It has been mentioned that the developed carbozirconation also has a potential application to the regio- and stereoselective synthesis of oHgosubstituted alkenes [79]. A consistent extension of this work disclosing the appUcation of the Negishi reagent [81] in carbometallations of alkynylboronates has been pubHshed recently (Scheme 10.99) [82]. 

Intramolecular co-cyclisation of 1,6- and 1,7-enynes using the Negishi reagent 4 gives bicyclic zirconacyclopentenes 18 in excellent yields (Scheme 5.7). An Ti -alkyne complex 17 is likely to be the first formed intermediate. 

The divalent Cp2Zr(II) species (zirconocene, Cp = / -C5H5) has been proved to be synthetically very useful for organometallic chemistry, synthetic chemistry, and polymer chemistry [2-14]. Zirconocene species include the Negishi reagent... 

Cp2ZrBu2 (Negishi reagent), as a very useful zirconocene (II) species, can be easily generated in situ from Cp2ZrCl2 and two equivalents of n-butyl lithium in toluene at -78 °C for 1 h [7]. Zirconocene (II) species promoted intermolecular coupling of... 

The construction of the cyclobutane of 1 was effected by an interesting application of the Negishi reagent (Cp ZtCyi x BuLi). Complexation of Cp Zr with the alkene followed by elimination generated an allylic organometallic 11, which added to the released aldehyde to give the cyclobutanes 12 and 13 in a 2.4 1 diastereomeric ratio. 

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