Sequential Catalysis Involving Metal-Catalyzed Cycloisomerizations and Cyclizations

Sequential Catalysis Involving Metal-Catalyzed Cycloisomerizations and Cyclizations 

Metal-catalyzed domino reactions are characterized by organometallic specimens that are regenerated in multiple insertion events and yield after an elimination step the complex, often polycyclic organic product. Predominantly in palladium chemistry, unimolecular reactions proceeding in an intramolecular fashion, for example, by cyclic carbopalladation [5], furnish complex polycyclic structures starting from linear polyunsaturated substrates. 

Two prerequisites for successfully performing sequentially catalyzed processes can be easily identified. As in domino reactions, the initial catalyzed process has to generate or retain a functional group that is suitably reactive for a subsequent transformation. And the catalyst or catalyst precursor has to be present in the reaction medium during the whole sequence without further addition of the transition-metal source after the initial step. Triggering additives might be added from step to step. 

In the past decade, cycloisomerizations and cyclizations have received particular attention as processes with a high degree of atom economy. Linear precursors are cychzed, and an increase of molecular complexity is induced in the initial step. On the other hand, the effective catalyst system still stands available for further catalytic transformations. 

Sequential transition-metal-catalyzed processes are dominated by palladium-17], rhodium- [8], and ruthenium- [9] catalyzed sequences. With respect to Fogg s and de Santos classification, only cyclizing metal-catalyzed one-pot processes [1] in the sense of auto and assisted tandem catalysis will be discussed and highlighted in this overview. 

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I 12 Sequential Catalysis Involving Metal-Catalyzed Cycloisomerizations and Cyclizations... 

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