Direct Carbon-Hydrogen Bond Functionalization of Heterocyclic Compounds

This account summarizes our recent results on the direct carbon-hydrogen bond functionalization of heterocyclic compounds, including arylation, alkenylation, alkynylation, alkylation, and amination. In the arylation and alkenylation reactions, we mainly focus on the potential of less-expensive first transition elements and demonstrate the good activities of copper and nickel catalysts which are similar to those of conventional palladium ones. The catalytic systems based on copper or nickel also enable direct alkynylation with simple terminal alkynes, as well as with alkynyl halides. On the other hand, a new application of palladium catalysts in the relatively difficult direct alkylation is shown. In addition to the development of catalysts, we introduce chloramines as new, efficient electrophilic amination reagents for heteroaromatic carbon-hydrogen bonds; these compounds allow the concise synthesis of amino-substituted azoles that are of great interest in pharmaceutical and medicinal chemistry.