[GRAPHICS]Biaryl bromides such as 1 (R=NO2, H, OMe) undergo the Heck reaction to give both the expected products 3 ("retention") as well as "crossover" products 4 derived from a migration of Pd and net transfer of reactivity from one aryl ring to the other. Under the conditions used, crossover is increasingly favored when electron-deficient arenes are involved. Crossover products derived from transfer onto the pyridine ring have also been observed.
Intercepting Palladacycles Derived by C−H Insertion. A Mechanism-Driven Entry to Heterocyclic Tetraphenylenes
作者:David Masselot、Jonathan P. H. Charmant、Timothy Gallagher
DOI:10.1021/ja056964d
日期:2006.1.1
Mechanistic support for the intermediacy of a palladacycle, which has been implicated in the crossover Heck reaction, has been obtained by intercepting this species using biphenylene. This leads to the formation of heterocyclic tetraphenylene derivatives. Three examples of this process are reported, and in two cases, the product structures have been confirmed by X-ray crystallographic analysis.
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