Jt-allylnickel

That this comparison seems to have validity (neglecting the legitimated analogy between bis-JT-allylnickel and symmetry-reduced benzene) may be atMboted to the fact that open-chain TT-systems may display some residual aromaticity (see Ref. ). Metal complexes with C3 symmetry must have three identical ligands (S) in the same state. When we change only one l and (S versus L) symmetry is reduced. The structural consequence is the change to a T- or Y-shaped moiety (see Fig. 1 in Scheme 2.5-4 and similar discussions in Refs. Within thcK arran ... 

AUylbenzene, 86 Allyl benzoate, 26 Allyl chloride, 104 Allyl chloromethyl sulfide, 94 Allyl ethers, 246-247 Allylic alcohols, 150, 151-152, 328 Allylic chlorides, 151-152, 293 Allylic coupling, 211 Allylic hydroxylation, 246 Allylic oxidation, 35, 55-56, 171 2-Allylisopropyl bromide, 224 JT-Allylnickel bromide, 210 Allylphosphoric dichloride, 104 Alumina, 6... 

Jt-Allylnickel and -cobalt compounds insert perfluoroolefins. These are included here because u-alkyl complexes probably are the true reactants. Bis-(7r-2-methallyl)-Ni(II) gives an insertion followed by a reductive elimination producing a Ni(0) complex with tetrafluoroethylene and the 1,7-diene product as a ligand ... 

A nickel-catalyzed ene cyclization (sec. 11.13) has been reported that uses Ni(cod)2- The reaction proceeds by initial formation of a ac-allylnickel complex, which facilitates the intramolecular ene reaction with an allylic amine unit. l jt-Allylnickel complexes can be used in coupling reactions with both aryl and alkyl halides. Enolate anions react with nickel(O) reagents to form a complex that subsequently couples to aryl iodides. Semmelhack s final step in the synthesis of cephalotaxinone (446) treated 445 with Ni(cod)2 to... 

Insertion of norbornene into a C-M bond is often reversible. For example, a jT-allylnickel norbornene complex was in equilibrium with inserted alkyl-nickel species (Scheme 1.33) [41]. Whereas the chloride complex favored the ir-allylnickel form, the acetate complex favored the inserted alkylnickel species. 

Reaction of Jt-allylnickel, generated in situ from methyl vinyl ketone, MejSiCl and Nal, with a polarized alkyne in the presence of CO gives the corresponding cyclopentenone in moderate yield [185], When CO is introduced prior to the addition of the alkyne and with 2 lketone/alkyne stoichiometry, cyclopentenone is obtained regioselectively in high yield. In the absence of CO, cyclohexadiene derivative is obtained. When an excess amount of vinyl ketone is used, acyclic product is isolated predominantly. 

In a similar manner, three-component coupling of allyl chlorides or acetates with 1-alkynes and alkynyltins in the presence of a nickel catalyst prepared in situ from Ni(acac)2 and DIBALH provides a convenient regio- and stereoselective synthesis of 3,6-dien-l-ynes [231,232], It is interesting to note that no phosphine ligands are required in these reactions. A Jt-allylnickel intermediate is proposed. 

Similarly, reaction of dienes with COj in the presence of Ni(COD)2 affords Jt-allylnickel complex. Upon treatment with Me2Zn, the corresponding dicer-bonxylic acid is isolated. On the other hand, when the nickel intermediate is allowed to react with Hd, only monocarboxylation product is obtained [244]. Asymmetric induction is observed when (S)-MeO-MOP ligand is used [245,246]. 

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