Application of Isonitrile-Metal Complexes to Organic Synthesis

This account outlines our studies on isonitrile-metal complexes and their application to organic synthesis.Isonitriles possess an electronic structure which is similar to that of carbon monoxide. The carbene character brings about versatile reactivities as the reagent and interesting properties as the ligand. The α-hydorogen is highly acidic, and hence, the α-position is endowed with a nucleophilic character. Reduction of an alkylisonitrile with tin hydride affords alkane via a radical mechanism. Various organometallic reagents undergo α-addition to isonitriles and the resulting imidoylmetal intermediate acts as the acyl anion equivalent. Insertion of isonitriles into an Si-Si bond is catalyzed by palladium. A highly enantioselective aldol reaction of α-isocyanoesters with aldehydes is achieved by a gold catalyst. Isonitrile-Pd(0) complexes efficiently activate Si-Si and Si-B linkages, and unsaturated functionalities are inserted therein. Aromatizing polymerization of 1,2-diisocyanoarenes produces poly(quinoxaline)s which possess chiral helical structures. Enantiomerically enriched ones are successfully synthesized by using a chiral catalyst or auxiliary.