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2.11.5.B Applications of Product Subclass 5 in Organic Synthesis

DOI: 10.1055/sos-SD-002-00797

Negishi, E.-i.; Takahashi, T.Science of Synthesis, (20032754.

As in Section 2.11.4, there does not appear to have been any reported and recognized reactions of five-membered hafnacycles exhibiting clear-cut advantages over the corresponding zirconacycle reactions. In contrast with acyclic bis(η5-cyclopentadienyl)diorganozirconium derivatives discussed in Section 2.11.4.8, which tend to decompose via β-hydrogen abstraction, five-membered zirconacycles are thermally more stable. It should, however, be noted that five-membered zirconacycles are prone to decomposition via ring contraction. Indeed, many nucleophilic or basic reagents induce this ring contraction according to the general scheme shown in Scheme 89. With highly nucleophilic organolithiums, ate complexation and displacement of a cyclopentadienyl ligand are also possible, as discussed in Section 2.11.10. The relative stability of five-membered zirconacycles consisting only of zirconium and organo groups decreases in the order zirconacyclopentadienes > zirconacyclopentenes > zirconacyclopentanes.

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