Carbopalladation-cross-coupling tandem

The cyclic carbopalladation-cross-coupling tandem reaction has been extensively developed over the past several years. Despite earlier favorable findings with A1 and Zr [84], these metals are still scarcely used. On the other hand, organometals containing Sn and B have been widely used, and favorable results have been obtained for the formation of ffve-membered car-bocycles and heterocycles containing N and O from halodienes [88] (Eqs. 1 and 2 in Scheme 29), haloenynes [89-92] (Eqs. 3-5 in Scheme 29), haloaryl-alkynes [94,95] (Eqs. 6 and 7 in Scheme 29), and allenene derivatives [93,96] (Eqs. 8 and 9 in Scheme 29). 

Tandem cyclic carbopalladation cross-coupling process... 

Arylaluminums have not been used as extensively as some other arylmetals in Pd-catalyzed cross-coupling. However, the intrinsic reactivity of arylaluminums appears to be somewhere between that of Zn and Sn. It is this relatively low intrinsic reactivity of arylaluminums that is critically required in the cyclic carbopalladation-cross-coupUng tandem process shown in Scheme 44. The high intrinsic reactivity of Zn leads to the formation of the unwanted direct cross-coupling prodnct in 57% yield, while the corresponding reaction of PhSnBus does not produce either product under the conditions used. ... 

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