Metal-organic cooperative catalysis in C-C bond activation.

This review describes recent advances that have been made in studies of transition metal-promoted metal-organic cooperative C-C single bond activation reactions of unstrained organic substances, which use 2-aminopicoline as a temporal chelating ligand. In addition, metal-organic cooperative C-C double bond and C-C triple bond cleavage processes are discussed in association with transition metal-catalyzed C-H bond activation. Recent progress made in these areas has opened up the new paradigms in synthetic organic chemistry for the construction of organic frameworks by structural reorganization of organic backbones. Among the many strategies devised, chelation-assisted C-C bond cleavage reactions, which operate through cooperation between metal complexes and organic substances, have attracted perhaps the greatest attention. Utilizing this approach, efficient C-C single bond activation reactions have been developed for a variety of substrates, including linear alkyl ketones, secondary alcohols, primary amines, and cycloalkanones. In addition, reactions that lead to cleavage of C-C double and triple bonds can be facilitated by using the metal-organic cooperation strategy. C-C double bonds in α,β-enones can be cleaved by addition of cyclohexylamine, which facilitates Michael addition and retro-Mannich type fragmentation cascades proceeding via β-aminoketimine intermediates. Aldehydes, which serve as one of the fragmentation products of these processes, can be trapped by chelation-assisted hydroacylation reactions to produce ketones. Finally, C-C triple bond cleavage of alkynes can be achieved through hydroacylation reactions with aldehydes and subsequent C-C double bond cleavage of the resulting α,β-enones.