Carbocationic centers, skeletal rearrangements

When the two alkynyl functions are separated by a sUyl or a phosphano group, an interesting rearrangement takes place giving rise to tricyclic species (Scheme 30). This skeletal rearrangement proceeds via intermediate zwitterionic zirconate (102). The empty orbital and electrophilicity of Zr are probably the reasons that lead to zwitterionic species containing zirconates and carbocationic centers. 

Involvement of Pd-induced formation of dipolar intermediates has also been imph-cated in other Pd-catalyzed rearrangements. The dipolar intermediates in these reactions often contain carbocationic centers, which can participate in skeletal rearrangements. Those involving net oxidation are presented in Sects. V.3 and VIII.4, while those that lead to net isomerization are discnssed in Sect. IX.2.1.2. 

A. CARBON SKELETAL REARRANGEMENTS VIA 1,2-ANIONOTROPIC SHIFTS OF ORGANOPALLADIUMS CONTAINING CARBOCATIONIC CENTERS... 

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