Polysubstituted benzenes are useful building blocks for functional materials and biologically active molecules. Therefore, having a facile synthetic methodology for constructing these molecules is highly desirable.
A team led by Andy Hor and Jin Zhao of the Institute of Materials Research and Engineering of A*STAR in Singapore and National University of Singapore developed an effective catalyst system comprised of a simple nickel substrate, an easily accessible imidazolium salt, and a common Grignard reagent for the [2+2+2] cyclotrimerization of unactivated internal alkynes.
These preparative reactions proceeded under ambient conditions (room temperature or 60 °C) in only 20 or 60 min via in-situ-formed nickel N-heterocyclic carbene catalysts, giving excellent yields with high regioselectivity. The nature of the imidazolium salt significantly affected the catalytic activity and regioselectivity. The methodology opens an alternative and practical pathway to different polysubstituted benzenes, conjugated aromatic substances, functional dendrimeric materials and extends the application realm of nickel complexes in catalytic C–C bond formation reactions.
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