Nitriles cocycloaddition reactions

In this chapter we outline advances in the ruthenium-mediated alkyne [2 + 2 + 2] cycloaddition reactions. These can be classified into two major categories in terms of the types of products (1) syntheses of benzene derivatives via alkyne [2 + 2 + 2] cycloadditions and (2) syntheses of heteroaromatics via [2 + 2 + 2] cocycloadditions of alkynes with nitriles or heterocumulenes. Benzene ring-forming reactions are essentially prototypes of the corresponding heteroaromatic annulations. Therefore, the first class of reactions is reviewed in the next section and followed by a discussion of the second class of reactions. The mechanistic aspects and synthetic applications of ruthenium-catalyzed [2 + 2 + 2] cycloadditions are also described to exemplify the scientific and practical significance of ruthenium catalysis. 

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