Nickel-ene reactions

The above concept of catalytic metallo-ene cyclizations (Scheme 36) may also be extended to platinum and nickel, as one would expect in view of previous work on intermolecular nickel-ene reactions (cf. Section 1.2.2.4). 

The first indication, reported in 1971, for a nickel-catalyzed intramolecular allylation of an alkenic bond was the dimerization of butadiene to 2-methylvinylcyclopentane (263). This efficient transformation (90%) proceeded with 1.2 mol % of a Ni catalyst (prepared in situ from (Bu3P)2NiBr2 and BuLi) in the presence of methanol and presumably involves a nickel-ene reaction of (262) followed by a -elimi-nation of Ha (Scheme 55). 

Intermolecular metallo-ene reactions show interesting prospects when applied to strained or strongly polarized enophiles. Intramolecular versions, however, have proved to be far more powerful in the hands of synthesis-oriented chemists. Based on the criteria of (established and/or potential) utility in organic syndesis the following summary is focused on intramolecular magnesium-, palladium- and nickel-ene reactions. 

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