A new method for the synthesis of δ- and α-carbolines through Ni-catalyzed [2 + 2 + 2] cycloaddition of ynamide-nitriles or alkyne-cyanamides with alkynes has been developed. The catalytic system of NiCl(DME)/dppp/Zn with a low-cost Ni(II)-precursor was first utilized in Ni-catalyzed [2 + 2 + 2] cycloaddition reactions, and the in situ generated Lewis acid may play an important role for the successful transformation. Not only internal alkynes but also terminal alkynes undergo the desired cycloaddition reactions efficiently to furnish the carboline derivatives with wide diversity and functional group tolerance.
A Ni/BPh catalyzed [2+2+2] cycloaddition of alkyne-nitriles with alkynes has been developed, which provides an efficient route to fused pyridines under mild reaction conditions. Mechanistic studies indicate that an azanickelacycle via heterocoupling of an alkyne with a nitrile moiety is possibly formed as a key reaction intermediate. The Lewis acid catalyst is crucial to the successful transformation, which is suggested to promote the oxidative cyclization process.
A gold-catalyzed formal [3 + 2] cycloaddition of ynamides with 4,5-dihydro-1,2,4-oxadiazoles has been developed. The reaction provides a concise and regioselective access to highly functionalized 4-aminoimidazoles likely via the formation of an α-imino gold carbene intermediate followed by cyclization. 4,5-Dihydro-1,2,4-oxadiazole was found to act as an efficient N-iminonitrene equivalent in these reactions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.