Palladium-Catalyzed Cyclization Involving Carbopalladation of Arynes

2 Palladium-Catalyzed Cyclization Involving Carbopalladation of Arynes 

7i-Allylpalladium species can also participate in aimulation processes with arynes, yielding phenanthrene derivatives 234and235ina ratio of 58 42 (Equation 12.60) 

The reaction, initiated by carbopalladation of the aryne by stable ir-allylpalladium intermediates, is followed by the insertion of a second molecule of aryne into the arylpalladium bond and subsequent intramolecular carbopalladation of the alkene by the newly formed biarylpalladium species. When the second equivalent of aryne is replaced with an internal alkyne, naphthalene 236 is formed in a 47% yield (Equation 12.61). 

This palladium-catalyzed annulation has also been extended to arynes and 2-halobiaryls to synthesize fused polycyclic aromatic hydrocarbons (Equation 12.62) [130]. 

When one molecule of aryne precursor is replaced with a bicycUc alkene in the previous process, the carbocycUzation of an aryl iodide, a bicydic alkene and an aryne takes place, giving exclusively the eoco isomer of an annulated 9,10-dihydrophenanthrene 240 (Equation 12.65) [132]. 

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