Cross aryne, formation

Finally, Buszek and coworkers demonstrated that an appropriately substituted tri-bromo indole derivative such as 123 could undergo aryne formation and subsequent cycloaddition, followed by a metal-catalyzed cross-coupling reaction, to provide access to more complex structures (Scheme 33). As an example, a formal... 

Zirconocene-aryne complexes can also be transmetallated, opening the way to a broad spectrum of synthetic operations such as oxidation, halogenation and cross-coupling (Scheme 5). For example, transmetallation of zirconocene-aryne complex 26 with the palladium complex generated from Pd(0) and m-bromo(trifluoromethyl)benzene regioselectively affords palladium(ll) complex 27, which after reductive elimination can be iodinated to 28 [22]. Alternatively, treatment of 26 with B(OEt)3 results in the formation of 29, and its iodination and oxidation leads to 30 [23]. 

Guitiin, P6rez, and co-worlcers reported the palladium(0)/(/ )-BINAP complex-catalyzed enantioselective complete intermolecular cross-[2 + 2 + 2] cycloaddition of arynes with two dimethyl acetylenedicarboxylates for the preparation of a functionalized [5]helicene (Scheme 10.25) [24], Although the [5]helicene desired was obtained in low yield as a result of the formation of several isomers, relatively high enantioselectivity was observed (67% ee). 

---