Metalorganocatalysis: cooperating transition-metal catalysis and organocatalysis through a covalent bond

Asymmetric catalysis has grown rapidly and made considerable progress in the last few decades, but there still remain significantly unachievable reactions through either organocatalysis or transition-metal catalysis alone. The concept of combination of transition-metal catalysis with organocatalysis emerged as a powerful strategy for developing asymmetric catalysis, and has attracted great attention. In order to avoid the incompatibility existing in catalysts, substrates, intermediates and solvents through combining transition-metal catalysis and organocatalysis, it is urgently necessary to develop a new catalytic strategy to resolve these problems. Therefore, we are devoted to designing a series of novel bifunctional catalysts based upon the synergistic activation strategy via cooperating transition metal-catalysis and organocatalysis through a covalent bond forming a bifunctional molecule. In this review, this momentous strategy is illustrated with several recent outstanding examples and prospective promising applications, with the aim of elaborating the synthetic utilities and potentialities of this concept as a powerful tool in organic synthesis.