Palladium-Catalyzed Synthesis of Amidines via tert-Butyl isocyanide Insertion

C-H functionalization enabled by multiple isocyanides

Past decades have witnessed significant advance of isocyanides as a class of versatile organic synthons as well as their broad applications in multi-component reactions (MCRs) and other tandem reactions. Reactions involving multiple isocyanides allow the construction of molecules with further diversification and complexity, while C-H functionalization emphasizes the advantages of high atom economy, broad substrate availability and great synthetic efficiency. This promising synergistic strategy of C-H functionalization involving multiple isocyanides provides a variety of valuable synthetic methods for organic chemists' toolbox and offers considerable potential in pharmaceutical chemistry and materials science as well. The present review outlines in detail various reaction types of C-H functionalization enabled by multiple isocyanides, and the relevant mechanistic rationale is discussed.

De Novo Synthesis of α-Ketoamides via Pd/TBD Synergistic Catalysis

Precisely controlling the product selectivity of a reaction is an important objective in organic synthesis. α-Ketoamides are vital intermediates in chemical transformations and privileged motifs in numerous drugs, natural products, and biologically active molecules. The selective synthesis of α-ketoamides from feedstock chemicals in a safe and operationally simple manner under mild conditions is a long-standing catalysis challenge. Herein, an unprecedented TBD-switched Pd-catalyzed double isocyanide insertion reaction for assembling ketoamides in aqueous DMSO from (hetero)aryl halides and pseudohalides under mild conditions is reported. The effectiveness and utility of this protocol are demonstrated by its diverse substrate scope (93 examples), the ability to late-stage modify pharmaceuticals, scalability to large-scale synthesis, and the synthesis of pharmaceutically active molecules. Mechanistic studies indicate that TBD is a key ligand that modulates the Pd-catalyzed double isocyanide insertion process, thereby selectively providing the desired α-ketoamides in a unique manner. In addition, the imidoylpalladium(II) complex and α-ketoimine amide are successfully isolated and determined by X-ray analysis, confirming that they are probable intermediates in the catalytic pathway.

Recent Advances in Palladium-Catalyzed Isocyanide Insertions

Isocyanides have long been known as versatile chemical reagents in organic synthesis. Their ambivalent nature also allows them to function as a CO-substitute in palladium-catalyzed cross couplings. Over the past decades, isocyanides have emerged as practical and versatile C1 building blocks, whose inherent N-substitution allows for the rapid incorporation of nitrogeneous fragments in a wide variety of products. Recent developments in palladium catalyzed isocyanide insertion reactions have significantly expanded the scope and applicability of these imidoylative cross-couplings. This review highlights the advances made in this field over the past eight years.