Palladium catalysis heterocyclization, reviews

For a review of the use of palladium catalysis in heterocycle synthesis, with a good summary of the authors work, see Sakamoto, T. Kondo, Y. Yamanaka, H. Heterocycles 1988,27,2225-49. 

For a review of the use of palladium catalysis in heterocycle synthesis, with a good summary... 

The use of palladium catalysis to synthesize aromatic heterocydes has been reviewed in a number of recent publications [1], As such, rather than a complete discussion of this large field, the thrust of this review will be to highlight general examples of how palladium catalysis has become used in heterocyde synthesis. This will focus on routes that direcdy assemble the aromatic heterocyclic core, rather than their subsequent functionalization or the use of palladium to assemble precursors for traditional cydocondensations, and on processes that involve generation of carbon-heteroatom bonds. 

Af-Heterocyclic carbenes and phosphine ligands can bind metal centers in a somewhat similar feshion via dative coordination using a lone pair of electrons. Therefore, phosphines are often considered to be the closest neighbors to NHCs in terms of organometallic chemistry. However, the properties of these two classes of compounds can be quite different, and can yield, for example, catalysts with quite different reactivity. The use of NHCs in olefin metathesis [25] and in palladium catalysis [26], for example, has allowed the preparation of highly active and stable species that are now at the forefront of their fields. Various studies have been conducted to explore the nature of bonding between NHCs and metal centers. Diez-Gonzalez and Nolan reviewed some aspects of NHC coordination to metal centers in 2007 [27]. 

With ruthenium, palladium is arguably the most utilized transition metal for the synthesis of Af-heterocyclic carbene (NHC) complexes and definitely the most versatile for applications in catalysis. This chapter comprises the literature on NHC-Pd complexes since 2006, when the previous edition of this book was released, until the end of 2012. A search in Scopus on the topic Af-heterocyclic carbene palladium in this period yielded almost 550 references, including a number of specifically dedicated reviews [1-6]. We have focused in well-defined complexes, although some relevant in situ systems with interesting catalytic activity are also included. 

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