Pd(0)-Catalyzed Carboiodination: Early Developments and Recent Advances - New Trends in Cross-Coupling: Theory and Applications - page 315

the presence of tert-butyl acrylate to provide tandem coupling product
7.81 without any evidence of mono-Heck product 7.82 or monocyclization
product 7.80. The power of this method is highlighted by the
possibility of synthesizing numerous heterocycles and using many
different Mizoroki-Heck acceptors. In situ NMR studies revealed that both
the inter- and intramolecular transformations occur simultaneously and
that both resulting products converge on the desired Mizoroki-Heck/car-
boiodination adducts. This method can potentially facilitate the use of dif-
ficult polyhalogenated substrates, which are prone to cause catalyst
deactivation.
7.9 Conclusion
Palladium-catalyzed cross-coupling has become a practical and general
method in chemical synthesis. As a testament to the great impact that cross-
coupling reactions have had on our society, Professor Richard F. Heck,
Professor Ei-ichi Negishi and Professor Akira Suzuki were awarded the 2010
Nobel Prize in Chemistry. This intensely studied field has benefited from
continuous evolution since its inception. 111 Recently, the carbon-halogen
reductive elimination from transition metal complexes has come to light as a
potentially useful elementary step for use in catalytic cycles, a process
that was previously thought to be unachievable owing to unfavorable
energetics. Early and recent examples have led us to rethink the be-
havior of transition metal complexes containing both metal-carbon and
metal-halogen bonds. Rooted in the seminal reports by Ettorre and others,
this concept has significantly matured as a result of recent studies, par-
ticularly those of Hartwig and co-workers. Similarly to other elementary
transformations involving transition metals (i.e., oxidative addition and
transmetallation), stoichiometric experiments have been pivotal in our
gaining a sound understanding of how to achieve this reactivity. These re-
ports led to the realization of catalytic variants of carbon-halogen reductive
elimination by Buchwald and co-workers, in which aromatic carbon-halogen
bonds were formed during the step involving catalyst turnover. These aro-
matic Finkelstein-type reactions were followed up with a study by Lautens
and co-workers, where cross-coupling reactions involving reversible oxida-
tive addition to carbon-halogen bonds were conducted on polyhalogenated
substrates. In 2011, extensions to Pd-catalyzed sp 3 -hybridized carbon-
halogen bond-forming reactions were realized by both Lautens' and Tong's
groups. These reactions have emerged as an ecient method to synthesize
hetero- and carbocycles from simple starting materials. With the goal of
increasing the eciency of these reactions and their corresponding
catalysts, future studies will need to focus on catalyst development based on
mechanistic analysis. The field awaits further contributions from the
organic, inorganic and organometallic communities, who can advance our
understanding of this elementary catalytic transformation and its use in
synthesis.